TN295 
.U4 

No. 8947 



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Bureau of Mines Information Circular/1983 




Safety in the Use and Maintenance 
of Large Mobile Surface Mining 
Equipment 

Proceedings: Bureau of Mines Technology Transfer 
Seminars, Tucson, AZ, August 16, 1983, Denver, CO, 
August 18, 1983, and St. Louis, MO, August 23, 1983 

Compiled by Staff, Bureau of Mines 




UNITED STATES DEPARTMENT OF THE INTERIOR 



fAU^Md^. lU^f^P^^ 



Information Circular 8947 

/A 



Safety in the Use and Maintenance 
of Large Mobile Surface Mining 
Equipment 

Proceedings: Bureau of Mines Technology Transfer 
Seminars, Tucson, AZ, August 16, 1983, Denver, CO, 
August 18, 1983, and St. Louis, MO, August 23, 1983 



Compiled by Staff, Bureau of Mines 



UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



V -' 









This publication has been cataloged as follows: 



Bureau of Mines Technology Transfer Seminars (1983 : 
Tucson, AZ, Denver, CO, and St. Louis, MO) 

Safety in the use and maintenance of large mobile surface mining 
equipment. 

(Information circular / Bureau of Mines ; 8947) 

Contents: Introduction / by Wm. Thomas Cocke— Solving the problem 
of getting on and off large surface mine mobile equipment/ by Dennis A. 
Long— Collision protection technology / by William C. Yates- [etc.] 

Supt. of Docs, no.: I 28.27:8947. 

1. Strip mining— Safety measures— Congresses. I. United States. Bu- 
reau of Mines. II. Title. III. Series: Information circular (United States. 
Bureau of Mines) ; 8947. 



TN295.U4 [TN291] 622s [622'. 31'0289] 83-14429 



PREFACE 

This Information Circular summarizes recent Bureau of Mines research 
results concerning improved safety and health in the operation of large 
mobile surface mining equipment. The papers are only a sample of the 
Bureau's total research effort in this area, but they outline major por- 
tions of the program. 

Eight of the ten technical papers reproduced here were presented at 
Technology Transfer Seminars on Safety in the Operation and Maintenance 
of Large Mobile Surface Mining Equipment given in August 1983 in Tucson, 
AZ, Denver, CO, and St, Louis, MO. Those desiring more information on 
the Bureau's surface mine health and safety programs in general, or in- 
formation on specific situations, should contact the Bureau of Mines 
Division of Health and Safety Technology, 2401 E St., NW, , Washington, 
DC 20241, or the appropriate author listed in these proceedings. 



CONTENTS 

Page 

Preface 1 

Abstract « 1 

Introduction, by Wm. Thomas Cocke 2 

Solving the Problem of Getting On and Off Large Surface Mining Equipment, by 

Dennis A. Long 3 

Radio Wave-Transponder Collision Protection System, by William C. Yates, 

Guy A. Johnson, and James J. Olson 17 

Novel Truck-Design Concepts , by Guy A, Johnson , 30 

Operator Alertness Studies, by Richard J. Wilson 34 

Large ROPS and Operator Restraint Device Research, by Stephen A. Swan 45 

Off-Highway Haulage Truck Maintenance Safety, by Dennis A, Long «... 55 

Performance-Based Training for Mobile Equipment Operators, by Brett Collins, 

Kris Krupp, and Richard L. Unger 63 

Stability Indicators for Front-End Loaders, by Gilbert Wray and 

August J. Kwitowski 67 

Bulldozer Noise Control, By R. C. Bartholomae and T. G. Bobick 81 

Improved Haul Road Berm Design, by Gregory G. Miller, Gary L. Stecklein, and 

John J. Labra 87 



SAFETY IN THE USE AND MAINTENANCE OF LARGE MOBILE 
SURFACE MINING EQUIPMENT 

Proceedings: Bureau of Mines Technology Transfer Seminars, 

Tucson, AZ, August 16, 1983, Denver, CO, August 18, 1983, 

and St. Louis, MO, August 23, 1983 

Compiled by Staff, Bureau of Mines 



ABSTRACT 

These proceedings consist of papers presented at Bureau of Mines Tech- 
nology Transfer Seminars in August 1983 for the purpose of disseminating 
recent advances in mining technology in the area of large mobile surface 
mining equipment safety and health. The Bureau of Mines conducts sev- 
eral of these seminars each year in order to bring the latest results of 
Bureau research to the attention of the mining industry as quickly as 
possible. 



INTRODUCTION 
By Wm. Thomas Cocke 1 



Problems relating to the operation of 
large mobile surface mining equipment 
were addressed in a Bureau of Mines Tech- 
nology Transfer Seminar on Safety in the 
Operation and Maintenance of Large Mobile 
Surface Mining Equipment, The following 
papers were either presented at the semi- 
nar or relate to the subject. The topics 
covered are ingress-egress safety, colli- 
sion avoidance, novel truck design, oper- 
ator alertness studies, ROPS, operator 

^Staff engineer. Office of Technical 
Information, Bureau of Mines, Washington, 
DC. 



restraint devices, maintenance safety, 
operator safety training, improved haul 
road berm design, stability indicators 
for front-end loaders, and retrofit noise 
control for bulldozers. 

The objective of the Bureau of Mines is 
to improve technology and make it cost 
effective so that its acceptance and use 
by the mining industry will occur volun- 
tarily. For the results of Bureau re- 
search to be used, those results must be 
disseminated. That is the purpose of 
Technology Transfer Seminars. 



SOLVING THE PROBLEM OF GETTING ON AND OFF LARGE SURFACE MINING EQUIPMENT 

By Dennis A. Longi 

ABSTRACT 



Slip and fall accidents are a major 
cause of lost-time injuries associated 
with large mobile equipment in surface 
mines. An evaluation of the safety haz- 
ards associated with ingress and egress 
on these vehicles showed that most of the 
accidents occur at the point where per- 
sonnel attempt to mount or dismount the 
machine at ground level. The major haz- 
ardous design conditions were identified 
as excessively flexible supports for low- 
er steps or rungs, inappropriate ground- 
level-to-first-step distances, poor step 



designs, access designs that use machine 
components as steps or walkways, and in- 
adequate handrail and guardrail designs. 
Additional hazards are introduced by the 
lack of proper maintenance of ladder 
hardware and the work practices of opera- 
tors in carrying articles onto the truck. 
Several improved systems were designed 
and tested for accessing large mobile 
mining equipment. These new systems have 
undergone long-term testing in operating 
mines. 



INTRODUCTION AND STATEMENT OF THE PROBLEM 



Mobile equipment manufacturers and min- 
ing companies both recognize the problem 
of getting on and off the large mining 
equipment operating in today's surface 
mines. Overall, there is a lack of de- 
sign standards for ingress and egress 
systems, as evidenced by the diversity of 
ladder designs, and access systems appear 
to be added as an afterthought to the 
overall equipment design. In short, the 
system design concepts employed for most 
of the machine features are not generally 
applied in ladder access system designs. 

The Bureau of Mines awarded contracts 
for on-site reviews to identify design 
deficiencies associated with access lad- 
ders currently used in operating surface 
mines. These reviews focused on handrail 
designs, step and ladder designs, ladder 
and step placements, ground clearance 
problems, environment-induced problems, 
and other factors. 

Mining engineer. Twin Cities Research 
Center, Bureau of Mines, Minneapolis, MN. 



This research identified the following 
significant ingress and egress system de- 
sign deficiencies: 

1. Inadequate handrail and guardrail 
designs that increase the difficulty of 
mounting and dismounting the vehicle. 

2. Excessively flexible lower section 
supports for lower steps or rungs on lad- 
ders that make ascent or descent diffi- 
cult and hazardous. 

3. Inappropriate ground-level-to-first- 
step distances that require personnel 
to take unsafe positions to climb onto 
equipment. 

4. Step designs that permit mud, snow, 
ice, grease, and oil accumulations and 
thus result in hazardous footing. 

5. Access systems that require the use 
of equipment components as primary steps, 
such as the track on dozers and shovels. 



The ingress-egress problem involves two 
distinct mobile equipment types. The 
first category includes haulage trucks 
and front-end loaders. These vehicles 
utilize either vertical or nearly verti- 
cal ladder access systems positioned in 
the vicinity of the cab. Analysis has 
shown that the chief hazards in the lad- 
der designs are found in the first steps 



of the ladder, where the operator mounts 
or dismounts the machine. The second 
category includes tracked vehicles, such 
as dozers, shovels, and draglines. These 
vehicles have one common hazard: The 
primary access system usually involves 
using the track component as a step or 
walkway . 



SAFETY HAZARD ASSESSMENT 



Evaluation of the safety hazards asso- 
ciated with mobile equipment in surface 
mines confirmed that slip and fall acci- 
dents account for a substantial propor- 
tion of vehicle-related accidents. Slips 
and falls while ascending or descending 
the machines constitute over one-third of 
all lost-time accidents associated with 
the operation of haulage trucks, front- 
end loaders, track dozers, shovels, and 
draglines. These five equipment types 
account for 80 pet of the mobile equip- 
ment found in U.S. surface mines. 

A review of Mine Safety and Health Ad- 
ministration data revealed that almost 
2,000 slip and fall accidents occurred on 
surface mine mobile equipment during the 
1978-79 2-year period. These accidents 
accounted for almost 30,000 lost employee 
days. The average slip and fall resulted 
in 15.3 lost days. The characteristic 



injuries resulting from ingress-egress 
activity are cuts, lacerations, contu- 
sions, fractures, sprains, and strains. 
The hands, fingers, back, legs, and feet 
are the body parts most frequently in- 
jured in these accidents. 

The slip and fall accident reports were 
further analyzed to determine where in 
the process of mounting or dismounting 
the machine operators or maintenance per- 
sonnel are getting hurt. This further 
breakdown revealed that over 40 pet of 
all surface mine slip and fall accidents 
were attributable to the first step onto 
the vehicle as the operator attempted to 
mount or dismount the vehicle. The haz- 
ard is greater on track dozers, which ex- 
perience nearly 60 pet of all .slip and 
fall accidents occurring during the at- 
tempt to mount or dismount the vehicle. 



HAULAGE TRUCKS AND FRONT END LOADERS 



CURRENT DESIGN PROBLEMS 

Off-highway haulage trucks usually have 
ladders mounted on the front of the truck 
adjacent to the left side of the engine 
compartment (figs. 1-2), with the angle 
of inclination between 75° to 90° (verti- 
cal) , On some truck models the bumper is 
used as part of the ladder structure 
(fig. 3), The ladders used on almost all 
front-end loaders are located directly 
alongside the cab. Some front-end load- 
ers use movable or retractable ladders in 
which the operator must pull down the 
ladder unit to mount the vehicle. 



The problem of vehicle ground clearance 
is critical within the open pit mine en- 
vironment, and mobile mine vehicles are 
typically designed to ensure about 3 ft 
of ground clearance. However, the lower 
portion of the primary ladder assembly 
must be below this level for the operator 
to reach the first step, which places the 
first two steps in a vulnerable position 
at the front corner of the truck. At 
this position the ladders are subjected 
to frequent damage from objects in the 
roadway and from striking guide berms or 
other obstructions. 




FIGURE 1. - Typical ladder on off-highway haulage truck. 




FIGURE 3. - Truck ladder using bumper as part of ladder system. 




FIGURE 4. - Wire-rung lower truck ladder. 



The prevalent solution to this problem 
is to suspend the lower one or two steps 
on a cable which is then mounted to the 
bumper or the rigid section of the lad- 
der. These wire rope or cable steps are 
invariably knocked out of position and do 
not return to their initial configuration 
(figs. 4-5). The height of the lower 
rung above the ground ranges between 36 
and 42 in. The flexible ladder supports 
for the lower steps, and the fact that 
they are still too high for the operator 
to safely mount and dismount the machine, 
contribute to slipping and falling 
accidents, 

DEVELOPMENT OF AN IMPROVED, 
SPRING STEP LADDER 

In 1978 the Bureau of Mines began 
work to design and develop improved 



ingress-egress systems for surface mine 
mobile equipment, with the primary goal 
of solving the problem of lower ladder 
design. Several primary lower ladder 
designs were subjected to human factors 
field evaluation and structural test- 
demonstrations. As a result of 



ing 



the 



intial field demonstrations, the Bureau 
concluded that a four-spring design 
(figs. 6-7) could appreciably reduce 
slip and fall accidents on haulage trucks 
and loaders. The prototype lower steps 
substantially reduced the height of the 
first step and were much more rigid when 
stepped on or off. Because of their high 
stiffness coefficient and the preten- 
sioning of the springs, the prototype 
lower steps closely maintained both step 
distance and angular inclination of the 
ladder. 




FIGURE 5. - Closeup of wire-rung lower truck ladder. 



10 



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FIGURE 6. - Bureau of Mines spring step 



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FIGURE 7. - Bureau of Mines spring step striking a boulder 



11 



Since 1978 some 30 spring steps have 
been field-tested at 13 mines on 27 sur- 
face mine vehicles. The maintainability 
of the spring ladders varied widely from 
mine to mine. At some mines the ladders 
sustained damage after 3 or 4 weeks, 
while at other mines, ladders remained 
on the trucks with little or no damage 
for more than a year. Failure of the 
spring step occurred owing to a variety 
of reasons. The most common reasons 
included shear at the point where the 
step is welded to the ladder, spring 
failure resulting from low ground clear- 
ance, and lack of operator or supervisory 
acceptance. 

The results of the field testing indi- 
cated that the pretensioned spring step 
was a viable solution to the first-step 
access problem. However, the testing al- 
so showed that proper installation tech- 
niques, correct vehicle applications, and 
positive management support were impor- 
tant for long-term spring step survival. 



Proper supervision and management sup- 
port is essential for long-term success. 
Some of the test units that might have 
realized longer life through simple main- 
tenance and repair were quickly replaced 
with the traditional "home-made" steps 
at the slightest sign of failure. Opera- 
tor acceptance is also important, because 
in several cases it seems that the vehi- 
cle operator was putting the step to 
the test. The spring step unit is not 
indestructible. 

HOW IT WORKS 

The spring ladder concept is shown in 
figure 8. The unit consists of two 
steps constructed from grip strut materi- 
al to minimize the accumulation of debris 
and provide an antiskid surface for good 
footing. The steps are joined with two 
pairs of spring assemblies and mount- 
ing brackets. The mounting brackets con- 
sist of a flat plate and a collar to sup- 
port the spring, which is welded to the 









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HIGH-GRIP STEP* 
MATERIAL (TYPICAL) 



PRETENSIONED SPRING 
ASSEMBLY (TYPICAL) 



FIGURE 8. • Bureau of Mines pretensioned four-spring step. 



12 



flat plate. The springs are fabricated 
from stainless steel and pretensioned to 
150 lb. 

The spring step is a totally passive 
system and needs no activation by the op- 
erator. The steps support the weight of 
the operator with less than 2 in deflec- 
tion. The ground clearance required for 
rigid ladders mounted on large mining 
equipment is commonly 36 to 54 in. Owing 
to the flexible and durable spring- 
mounted supports, the new ladders can be 
mounted with the bottom step about 30 in 
above the ground. 

Other applications are also available 
for the spring step concept. On two 
trucks, a single-step spring ladder was 
installed in place of the standard oil 
check step. These ladders experienced no 



damage during the program; however, these 
steps were mounted in a more protected 
area under the engine compartment. On 
certain lower capacity front-end loaders 
and haulage trucks, a single-step ladder 
was installed to extend the existing 
ladder. 

The Bureau has made significant im- 
provements in design and fabrication 
since the first version of the spring 
step. As a result of long-term in-mine 
testing, a new, more durable pretensioned 
spring step has been fabricated. The 
lower ladder unit has a modular design, 
allowing replacement of individual parts. 
Wherever possible, the double spring step 
should be used for optimum survivability. 
The improved ladders can be installed at 
reasonable cost on operating trucks or 
new ones. 



TRACK DOZERS AND SHOVELS 



CURRENT DESIGN PROBLEMS 

Over the past decade, the size of track 
dozers in surface mines has increased 
substantially. Today operators must 
climb up 4 ft or more to mount the dozer. 
In most instances they must step onto or 
climb over the track assembly (fig. 9). 
Because of the harsh working environment 
encounterd by the dozer, the tracks are 
often covered by mud, snow, or ice, mak- 
ing them an unsafe access way. 

The ladder and stair units used on min- 
ing shovels and draglines vary in quality 
of design and safety. Many large excava- 
tors use electrically or hydraulically 
operated stairways for access up to the 
main decking or cab. Small to medium ma- 
chines often utilize several variations 
of pulldown ladders or counterbalanced 
stair-type units (fig. 10). 

The Bureau's work determined that an 
improved access system for tracked vehi- 
cles would result in a safer method of 
transporting personnel and materials up 
and over the track assembly. 



DEVELOPMENT OF THE POWERED 
SAFETY STEP 

In 1976 the Bureau chose to evaluate 
the powered safety step designed by Ted 
Rivinius, The work, conducted on a cost- 
sharing basis with Rivinius, included the 
development and fabrication of the pow- 
ered safety step design. Then in-mine 
tests were conducted to determine sur- 
vivability of the step prototype in the 
rugged mine environment and the potential 
for improved safety. 

Mine installations of 35 powered safety 
step production units have proven conclu- 
sively that the unit provides safer ac- 
cess to tracked mining vehicles. Five of 
these powered step units eventually 
failed during the mine testing. One step 
failed after 5 yr, three failed between 1 
and 2 yr, and one step lasted only sev- 
eral weeks. The steps that failed were 
tested on haulage trucks, scrapers, or 
dozers which must work in close, confin- 
ing conditions. 



13 



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FIGURE 9. - Typical track dozer 




FIGURE 10. - Typical loading shovel. 



14 



To date 30 powered step units are still 
in active use as installed on the ma- 
chines. Several step units have seen 
over 5 yr of continued use. Current in- 
stallations of the powered step include 
18 loading shovels, 9 track dozers, 2 
graders, and 1 dragline. The mines have 
reported that maintenance is surprisingly 
low and survival is high. As with any 
prototype safety hardware, successful ap- 
plication of the powered step depends 
greatly on management support and 
supervision, 

HOW IT WORKS 

The powered safety step is a hydraul- 
ically powered device to lift personnel 
and materials from the ground to working 
levels on large equipment (figs, 11-12), 
The primary application of the powered 
step is on the large track dozers, shov- 
els, and draglines. The powered unit 
eliminates hazardous blind steps and 



makes it unnecessary for operating per- 
sonnel to climb on irregular surfaces, 
such as the track or push arm. 

The powered safety step is powered by 
a self-contained electric-hydraulic unit. 
Power comes either from the vehicle's 
auxiliary power supply or from the step's 
own battery source, depending on the ap- 
plication. When in the "down" position, 
the step rests approximately 15 in from 
ground level. When the machine is op- 
erating, the step is automatically locked 
in the "up" position, protecting it 
against any damaging contact with ob- 
structions. Visual alarms and machine 
interlocks are provided where necessary 
to prevent machine operation when the 
step is in the "down" position. On ro- 
tating machines, such as draglines and 
shovels, an electrical interlock is pro- 
vided to prevent operation of the swing 
motors when the step is down. 




FIGURE 11. - Powered safety step on a loading shovel. 



15 




FIGURE 12. - Powered safety step on a track dozer. 



16 



To operate the step, the unit is acti- 
vated with an electrical switch located 
on the step. A single cylinder attached 
between two lifting arms smoothly lifts 
the step. The step is lowered by acti- 
vating a pressure-release solenoid. An 
in-line orifice controls downward speed 
and prevents free fall. On most ma- 
chines, additional control switches are 
located at ground level and in the opera- 
tor's cab. 

There are two basic designs of the pow- 
ered safety step. One operates only 



in two dimensions in the "up" and "down" 
directions. The second, using a link- 
age and bearing arrangement on the 
mounting end of the lift arms, rotates 
the step towards the machine in con- 
junction with the lifting motion. Thus, 
the step moves in an arc from ground to 
platform level. Each design is suited 
for specific applications. With minor 
modifications, a powered step can be 
adapted to any type or model of large 
machinery. 



AVAILABILITY 



Construction drawings, specification of 
materials, and other information are 
available for both the pretensioned 
spring step and the powered safety step. 



For information contact Twin Cities Re- 
search Center, Bureau of Mines, 5629 Min- 
nehaha Ave. South, Minneapolis, MN 55417. 



17 



RADIO WAVE-TRANSPONDER COLLISION PROTECTION SYSTEM 
By William C, Yates, 1 Guy A. Johnson, 2 and James J. Olson3 

ABSTRACT 



In cooperation with the Anaconda Copper 
Company, the Bureau of Mines developed 
and in-mine, on-vehicle, proof -of -concept 
tested a prototype, interactive radio 
wave-transponder system as a method of 
improving collision protection for large 
mobile mining equipment. The system uses 
detuned radio wave generators mounted on 



small mine vehicles to generate continu- 
ous radio waves. When the small vehicles 
are within the front-right or rear blind 
areas of a large haulage truck, the radio 
waves are detected by transponder units 
mounted on the truck. The prototype sys- 
tem then warns the haulage truck driver 
of a potential collision. 



INTRODUCTION 



This paper updates technology develop- 
ment efforts previously reported4 and 
involves a follow-on evaluation, conduct- 
ed on a cooperative basis by the Ana- 
conda Copper Company and the Bureau of 
Mines, of a second-generation prototype 
collision protection system at the Twin 
Buttes Mine south of Tucson, AZ. This 



project is a part of the Bureau's pro- 
gram to develop reasonably priced, relia- 
ble collision protection technology. The 
prototype hardware tested at the Twin 
Buttes Mine represents the most success- 
ful proof -of-concept testing completed to 
date. 



INSTRUMENTATION 



DESCRIPTION OF RADIO WAVE- 
TRANSPONDER SYSTEM 

The prototype instrumentation tested 
constitutes an interactive radio wave 
transponder system designed by Bureau and 
Anaconda engineers during the past few 
years. The system works by using rug- 
gedlzed detuned radio wave generators 
mounted in small mine vehicles. Radio 
waves continuously sent by small vehicle 
are sensed by transponder units mounted 

Process control engineer. Anaconda 
Minerals Co., Tucson, AZ. 

^Supervisory mining engineer. Twin Cit- 
ies Research Center, Bureau of Mines, 
Minneapolis, MN. 

■^Deputy research director. Twin Cit- 
ies Research Center, Bureau of Mines, 
Minneapolis, MN. 

^Yates, W. C. Development and Eval- 
uation of Pit Truck Safety Devices. 
Pres. at SME-AIME Ann. Meeting, Feb. 14- 
18, 1982, Dallas, TX, SME Preprint 82-16, 
7 pp. 



on the right front and rear of large 
haulage trucks. The truck driver is then 
alerted to possible collision hazards by 
warning lights and a buzzer in the cab. 
The key to making the system work is to 
keep the signals from the detuned genera- 
tor strong enough to be sensed by the 
transponder units, yet have the signals 
fade quickly enough with distance to 
eliminate false alarms. 

After the initial short-term, on- 
vehicle testing of the first-generation 
radio wave-transponder collision protec- 
tion system at Anaconda's Butte Mine in 
Montana in 1981, several changes were 
made to correct shortcomings identified 
during the testing at the Butte Mine, 
Three of the most significant changes 
were (1) to remount the receiver in a 
conductive enclosure with tabs to facili- 
tate easier mounting, (2) to change the 
antenna cable from coaxial to a two-wire 
shielded cable, and (3) to relocate the 
system's in-cab warning unit in a sepa- 
rate small box for ease in mounting. 



18 



INSTALLATION AT THE ANAMAX TWIN 
BUTTES MINE 

After laboratory checks of the improved 
system in fall of 1982, arrangements were 
made for installation of the system com- 
ponents on mine haulage and personnel 
vehicles at Twin Buttes. This second- 
generation prototype system included the 
following components: two dual-channel 
receivers, three low-frequency transmit- 
ters, four receiver antennas, two display 
panels and cables, four transmitter an- 
tennas complete with cable, and four re- 
ceiver antenna cables. 



the antenna. The cable to the front an- 
tenna was routed along the existing ca- 
bles by the instrument control housing, 
then forward and down to the antenna 
located on the radiator shroud. Standard 
tie wraps held the cables in place. 

Twenty-four-volt power for the receiv- 
ers was supplied from a pi-section filter 
in the haulage truck's electrical system. 
The voltage was switched from the truck 
electrical system. The power supply ca- 
ble shield was initially left disconnect- 
ed at the supply end. The receiver end 
was grounded to the receiver chassis. 



The two dual-channel receivers were in- 
stalled in two 150-ton-capacity haulage 
tracks, numbers 43 and 51. The major 
criterion of selection for the small ve- 
hicles was frequent encounters with haul 
trucks. Accordingly, two of the low- 
power transmitters were installed in 
pickup trucks used by the mine electri- 
cians, and the third was installed in the 
mine's radio service van. 

The receiver antennas were mounted to 
special brackets welded to the haul 
trucks. The antennas were about 6 ft 
high and were located on the front right 
(figs. 1-2) and the center rear (figs. 
3-4) of the haul trucks. The receivers 
were mounted under the buddy seat of the 
respective haul trucks and were secured 
with four 1/4-in bolts welded to the 
floor (fig, 5). Cab layouts dictated the 
installation of the system's display box- 
es in the respective trucks. The right 
side of the dash in unit 43 provided ade- 
quate space for the box and allowed ease 
of viewing by the driver (figs, 6-7), 
Dash space in unit 51 was limited, and 
the display box was mounted above the 
right door (fig, 8). This position is 
observed by the driver when the right 
backup mirror is used. 

Rear antenna cables were routed from 

the cab, following existing cables and 

hoses, down along the truck frame, over 

the rear axle housing to the location of 



The low-power transmitter-antenna sys- 
tem was mounted on the top of the two 
pickup trucks and the radio service van. 
A magnetic-mount base antenna was placed 
on the truck roof, roughly over the cen- 
ter of the passenger compartment. Co- 
axial cable was routed over the roof, 
down the back of the pickup cab, through 
an existing hole near the bottom of the 
cab, and under the floormat to the loca- 
tion of the transmitter, A speaker 
bracket was used to mount the transmitter 
to the dash (fig, 9), This location al- 
lows drivers to view the system-on light, 
which assures them that the transmitter 
system is functional. 

The installation of the instrumentation 
system and initial adjustments on the 
electronic components to allow startup of 
the in-mine testing program were com- 
pleted in early November 1982, The front 
distance adjustment for the two haul 
trucks was determined by the front blind 
area. This area varies depending on the 
size and brand of the truck. Typically, 
however, this distance was adjusted to a 
12-ft separation between receiver and 
transmitter antennas. 

The rear antenna separation was ini- 
tially adjusted to 25 ft, the maximum for 
the original receiver configuration. 
Later in the test program, the distance 
was increased to about 36 ft by modifying 
a jumper on the range detector board. 



19 




20 




FIGURE 2. - Front antenna, unit 51, 



21 




o 



22 




FIGURE 4. - Rear antenna, unit 43. 



23 




FIGURE 5. - Floor-mounted receiver. 



24 




FIGURE 6. - Display panel, unit 51, 



25 




26 




27 




FIGURE 9. - Pickup transmitter mount. 



28 



SHAKEDOWN TESTS 

Initial tests of the system disclosed 
an electrical "noise" problem with unit 
51, which generally affected only the 
rear antenna. This truck had a General 
Electric UHF communications transceiver 
mounted in the cab that uses a dc-to-dc 
switching inverter which emits large 
amounts of radio frequency interference. 
The interference appeared to mix with the 
collision protection system's internal 
frequencies and caused periodic false 



alarms. Unit 43, on the other hand, had 
a Motorola UHF communications transceiver 
which did not emit a high level of inter- 
ference. No false alarm problems were 
caused by this transceiver. 

A number of different remedies were 
tried on the system components onboard 
unit 51 to eliminate the noise problem. 
The most successful solution was to en- 
close the antenna wiring in conduit. 
This modification greatly reduced extra- 
neous radio wave signals. 



FIELD TEST RESULTS 



Because of operational schedules in the 
mine, the radio wave-transponder system 
on unit 51 was not tested during ore 
hauls. The components mounted on unit 43 
were subjected to a mine haulage test 
period of about 2 months. Although some 
false alarms did occur when the dynamic 
brakes on unit 43 were used, the problems 
did not seriously impact the field 
evaluations. 



and called a mechanic. Upon arrival at 
the scene, the mechanic found that the 
haul truck had nearly backed into an un- 
occupied pickup truck and had indeed 
stopped just in time to avoid a colli- 
sion. Considering that only two pickups 
and one haul truck had active prototype 
hardware, this encounter was rather for- 
tuitous and clearly demonstrated the val- 
ue of the collision protection system. 



The right-front alarm distance was ad- 
justed so as to activate prior to the 
disappearance of the small vehicle into 
the blind area of the haul truck. The 
rear alarm distance was established at 
about 39 ft. This distance, although ex- 
cessive on the sides of the truck, was 
necessary to provide adequate distance at 
the rear when the truck was backing. Be- 
cause the haul roads at Twin Buttes are 
quite wide, sufficient passing clearance 
was available so few alarms occurred as 
the haul truck and small vehicles passed. 
In more congested areas, such as the 
crushqr or shovel locations, more fre- 
quent alarms occurred. These, however, 
generally indicated that the small vehi- 
cle was approaching the haul truck too 
closely, and this is exactly the con- 
dition the collision protection system 
is engineered to sense. The final en- 
counter pattern used in the test is shown 
in figure 10. 

The ultimate test occurred when one of 
the mine personnel, unfamiliar with the 
ongoing tests, was assigned to drive unit 
43. He was engaged in backing when the 
alarm sounded. Not knowing the purpose 
of the signals, he stopped the vehicle 



Rear 

reception 

areo 




RADIO WAVE -TRANSPONDER 
FIGURE 10,- Radio wave-transponder receiver pattern. 



29 



CONCLUSIONS 



Mounting of the second-generation, pro- 
totype collision protection system at 
Twin Buttes was simple and straightfor- 
ward. No problems were encountered in 
the installation of either the receiver 
or the transmitter. One detail of par- 
ticular importance to prospective users 
is the requirement to cut the cables to 
the exact length needed to minimize noise 
pickup in the mine. 

The present alarm pattern and distance 
setting gave the operator adequate warn- 
ing of encroaching vehicles at the mine 
site. Operator acceptance was good. The 
only problem with the system was that of 
noise. Although a GE radio proved to be 
the principal source of noise, other 
sources, such as the dynamic brakes on 
the haul trucks, also caused some prob- 
lems. As it appears impossible to remove 
all sources of noise in such large and 
complex equipment , the only apparent 



practical solution to the noise problem 
is to increase the receiver noise immu- 
nity in as simple a manner as possible. 
Some gain on the signal-to-noise problem 
could be obtained by a slight increase in 
transmitter power with an accompanying 
decrease in receiver sensitivity. 

Proof-of-concept testing of this type 
of collision protection technology is now 
complete. Each mine wanting to utilize 
such automation technology will have to 
modify each system to site-specific con- 
ditions (weather, etc). As tests at the 
Twin Buttes Mine have made clear, the 
next generation of hardware must have 
considerably more noise immunity. Other 
design parameters in the present system 
appear adequate, and the system helped 
prevent a potentially serious mishap, the 
backing over of a mine personnel vehicle 
by a haul truck. 



30 



NOVEL TRUCK-DESIGN CONCEPTS 
By Guy A. Johnsoni 



ABSTRACT 



This paper summarizes a feasibility 
analysis of novel design concepts for 
large haulage vehicles. A preliminary 
design of a completely novel, 170- 
ton-capacity truck configuration is pre- 
sented as a case example. 



The objective of this study was to pro- 
duce cost-effective, novel truck designs 
that reduce the inherent dangers associ- 
ated with current designs of large haul- 
age units. The novel design technology 
provides industry with an alternative to 
retrofit technology. 



INTRODUCTION 



During any particular year in the sur- 
face mining industry, off-highway haulage 
trucks are involved in accidents account- 
ing for more fatalities and lost-time in- 
juries than any other type of mobile min- 
ing equipment. The accidents can take 
many forms , each with a different injury 
potential. Haulage trucks can collide 
with each other. They can collide with 
and run over smaller vehicles, other mine 
equipment, and even workers. The trucks 
can overturn while traveling the haul 
road or while unloading at the dump site. 
Operators can receive sprains, strains, 
cuts, and bruises as a result of being 
bounced around in the cab during haulage 

^Supervisory mining engineer. Twin 
Cities Research Center, Bureau of Mines, 
Minneapolis, MN. 



cycle operations. In addition, operators 
and other workers receive injuries as 
the result of slipping and/or falling 
while getting on and off the truck, or 
while performing maintenance or service 
functions. 

Table 1 summarizes off-highway haulage- 
truck-related injuries that occurred in 
surface mining operations during 1978 and 
1979. The data are classified according 
to accident type, location of the acci- 
dent, and total number of resulting fa- 
talities and nonfatal injuries. The data 
for this Bureau of Mines accident analy- 
sis were obtained from mining industry 
injury and illness reports submitted to 
and compiled by the Mine Safety and 
Health Administration (MSHA) , Health and 
Safety Analysis Center, Denver, CO. 



TABLE 1. - Surface mining haulage truck accident summary (1978-79) 





Location 


Result 


Accident type 


Haul 
road 


Dump 
site 


Load 
site 


Other 


Fatality 


Injury 


Collision with — 

Haul truck 


58 

13 





74 

20 

6 

214 

27 


10 
2 
1 
3 

39 



18 

12 


18 
5 

3 



35 
35 


3 

1 
1 

2 

I 

3 

27 

334 


3 
3 

1 
5 
11 






86 


Other vehicle or machine 
Electrical wire 


18 
1 




3 


Rollover. .,,,,,,,,..,,,,.. 


107 




20 


Fire 


9 


Operator injured in cab1.. 
Nonoperating events 


294 
408 


Total 


412 


85 


96 


376 


23 


946 



Excluding previous categories, 



31 



SHORT- AND LONG-TERM SOLUTIONS 



The Bureau of Mines, MSHA, equipment 
manufacturers, and mine operators have 
tried many approaches to reduce the grow- 
ing number of accidents associated with 
large haulage trucks. The Bureau first 
sponsored research to develop and test 
retrofit technology to improve visibil- 
ity systems, improve ingress-egress sys- 
tems, improve bumper designs, improve 
fire detection and suppression, and im- 
prove collision detection and avoidance. 



Longer term, high risk work was also ini- 
tiated to reduce the inherent hazards 
associated with current designs of large 
haulage trucks. All of these projects 
have been carried out in cooperation with 
mining companies , equipment manufactur- 
ers, and/or academic institutions to as- 
sure that the research results cost ef- 
fectively met the generic needs of the 
industry. 



DESIGN ALTERNATIVES 



Because of the poor field of vision af- 
forded operators of large haulage trucks, 
the trucks are frequently involved in ac- 
cidents such as front-right turns over 
unseen smaller vehicles, backing into 
other haulage vehicles, and backing over 
a dump. The field of vision afforded an 
operator is a function of the cab loca- 
tion in relation to other haulage truck 
structures. The field of vision can be 
improved through direct visual aids, such 
as mirrors or the recently developed 
Bureau of Mines, downward-looking, fres- 
nel lens blind area viewers. Other con- 
cerns regarding cab location are ingress- 
egress-related injuries and, to a lesser 
extent, operator injuries from being 
"bounced around" during travel. With 
these relationships in mind, seven novel 
cab location concepts were developed and 
evaluated. Five of the concepts involved 
relocating the cab on a typical rear-dump 
haulage truck. Two involved locating the 
cab in a completely different vehicle 
configuration. 



Details of the feasibility analysis 
are contained in the contract final re- 
port "Novel Cab Design Concepts To 
Improve Large Haulage Vehicle Safety" 
(contract J0295013) by Woodward Asso- 
ciates, a copy of which can be consult- 
ed at the Bureau's research centers in 
Minneapolis, MN, Denver, CO, Spokane, WA, 
and Pittsburgh, PA. 

The results of the evaluation indicated 
that safety would be improved only mar- 
ginally (and in one case, slightly im- 
paired) by relocating the cab from its 
present location on rear-dump configura- 
tions. Since greater safety potential 
could best be obtained by redesigning the 
entire truck structure, this second proj- 
ect objective was pursued. This work 
involved generating and evaluating the 
feasibility of a novel haulage truck con- 
figuration: a front-dumping, midengine, 
170-ton truck. 



CASE HISTORY EXAMPLE: A FRONT-DUMPING, MIDENGINE CONFIGURATION 



While attempting to maintain or exceed 
the performance and economy of ownership 
and operation parameters of current haul- 
age trucks, a preliminary design analysis 
was performed to address each of the ma- 
jor hazardous situations associated with 
haulage truck operations, as shown in ta- 
ble 2. Table 2 lists the safety features 
incorporated into the front-dumping mid- 
engine configuration shown in figure 1. 
Table 3 gives the general specifications 
of the novel vehicle's design. Complete 



design specifications are contained in 
the final report prepared by Woodward 
Associates. 

To generate the concept, a typical 
large haulage truck was first broken down 
to its major components (fig. 2). The 
components selected for further analysis 
were then packaged in a configuration 
that maintained high productivity poten- 
tial while also providing improved safety 
features (fig. 3). This design concept 



32 



TABLE 2. - Safety improvements 
of the design 

Situation Design feature 



Collision Increase in field of 

vision. 
Location of cab away 
from impact points. 

Rollover Cab location protected 

by body and frame. 
Wide stance, four- 
wheel independent 
suspension. 



Ingress-egress. . 

Operator secur- 
ity inside cab. 



Maintenance and 
service. 



Cab location (low). 

Truck, suspension. 
Seat design. 
Overall interior 

design. 
Isolated cab. 

Ease of access to all 
systems, components, 
and service ports and 
areas. 



TABLE 3. - General specifications 
of novel vehicle design 

Body capacity, cu yd: 

Struck 73 

2:1 heap 142 

Body capacity, tons.... 170 

Dimensions, ft: 

Height 17 

Width 22 

Length 42 

Wheelbase 20 

Turning circle, ft 83.5 

Weight, tons: 

Empty 170 

Loaded 340 

Engine: 

Type KTA-3067-C 

Gross horsepower 1,600 

Transmission GTA-15, W/GE776C 

Tires 40:00-57 




FIGURE 1." Front-dumping, midengine, 170-ton-capacity truck concept. 



33 



Engine 



Loading 
height 




FIGURE 2. - Major components of a typical 
large haulage truck. 



FIGURE 3. - Components of a safer, more pro- 
ductive novel haulage truck design concept. 



='^ 


rjJ-ll4J-U-lW|p 


r 


t" 


t 


- 


tr^ 




lis 


i 


— 


K^M=ML 




If' 


3.5' 




^ B ^ 


1 


t 


• 21' 


_* 






FIGURE 4. - Dimensions of the novel concept. 



FIGURE 5. - Anticipated direct field of view 
of the novel concept. 



utilized only components currently used 
by the manufacturing industry. Figure 4 
depicts the dimensions and front-dumping 
feature of the design concept. Figure 5 
shows the anticipated direct field of 
view from the cab of the vehicle. 
This improved field of view, plus the 



structural protection around the driver, 
will improve his or her safety. The mid- 
engine design, with its inherent ease 
of maintenance plus the improved field of 
view, should also make the vehicle more 
productive. 



CONCLUSION 



Although the history of off -highway 
haulage truck development indicates a re- 
sistance to innovation and change, novel 
design technology as exemplified by the 



170-ton-capacity haulage truck configura- 
tion developed in this case study can 
provide improved safety potential without 
sacrificing performance. 



34 



OPERATOR ALERTNESS STUDIES 
By Richard J. Wllsoni 



ABSTRACT 



Mobile mine equipment accidents attrib- 
utable to a lack of alertness on the part 
of the equipment operator are of growing 
concern to the mineral industry. An 
investigation into the potential for mon- 
itoring certain physiological factors as 
a means of determining states of de- 
creased alertness was undertaken by the 
Bureau of Mines, Various oculomotor 
activities such as eyeblink rates, eye 
closure duration, and the timing of 



eyeblinks relative to a presented stim- 
ulus were monitored. Changes in pupil 
size were also recorded. Both blink rate 
and eye closure duration proved to be 
sensitive to the nature of the task. 
Blinking was also found to be timed so as 
to least interfere with the incoming in- 
formation presented in the series of 
tests. Measures of pupillary diameter 
change were not found to be correlative 
to alterations in levels of alertness. 



INTRODUCTION 



Accidents attributable to inattentive 
or unalert operators of large mobile min- 
ing equipment are of growing concern to 
the mining industry. The ever-increasing 
size of loading and haulage vehicles 
magnifies both the severity and the cost 
of accidents associated with their 
utilization. 

An analysis of recent (1979-80) Mine 
Safety and Health Administration accident 
data revealed that mobile mine equipment 
accidents account for an estimated 20 pet 
of all fatal mining accidents (coal, non- 
coal, surface, and underground) (_3),2 In 
42 pet of these cases, inattention or 
lack of alertness was listed as a con- 
tributing cause to the fatality. This 
figure might actually double if accurate, 
reliable methods of determining the 
causes of accidents were available, 
Basic, long-term scientific investigation 
is required to identify methods and tech- 
nologies capable of remotely monitoring 
an operator's state of alertness and thus 
help eliminate a major cause of vehicle- 
related accidents, 

^Mining engineer. Twin Cities Research 

Center, Bureau of Mines, Minneapolis, MN. 

^Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this paper. 



Inattentiveness or lack of alertness 
can be defined as a state of mind in 
which a person is unable to respond 
appropriately to an unexpected situation. 
This broad definition covers the range of 
simple daydreaming to being asleep at 
the wheel. This lack of alertness may be 
caused by any number of factors including 
sleepiness, fatigue, the influence of 
alcohol or drugs, and emotional factors 
that have a deleterious effect on an 
individual's performance capabilities. 
It should be noted that in the ongoing 
research effort the causal factors are 
not under investigation. It is only the 
detection of the reduced state of alert- 
ness that is of concern, 

A review of the relevant literature was 
conducted to ascertain what has been done 
historically in the study of alertness. 
Most of the prior articles dealt with the 
causal effects noted previously. Little 
conclusive information that correlated an 
individual's state of alertness with some 
monitorable physiological factor was 
available. The two areas that appeared 
to offer some potential for serving as 
predictors of levels of impaired per- 
formance were oculomotor and pupillary 
phenomena. 



35 



OCULOMOTOR PHENOMENA 



Many investigations into various ocu- 
lomotor phenomena (eyeblinks, eye move- 
ments and closures, etc.) have been con- 
ducted. As early as 1927, Ponder found 
that under constant conditions individu- 
als tend to maintain a relatively con- 
stant rate of blinking (8), It was also 
reported that blink rates did not vary 
whether blinks were counted in total 
darkness, or in dim or normal lighting. 
Prior studies have also found a correla- 
tion between eyeblinks and a person's 
level of attention, Kennard concluded 
that blink rates increased during periods 
of inattentiveness and blinks occurred 
typically at the moment of relaxation of 
attention (_5 ) , Other studies have shown 
a decrease in blink frequency from the 
baseline rate during periods of increased 
mental activity (_1_) , Wide variability in 
results from numerous other studies, 
however, prevents drawing any universal 



conclusions concerning blink rates and 
attentiveness . 

The time at which blinks occur rather 
than blink rates has also been investi- 
gated, although to a lesser extent. Drew 
found that changes in difficulty of a 
task correlated with changes in the time 
distribution of eyeblinks (2) m Kennard 
reported that when subjects were given 
observation tasks, blinking was inhibited 
in all cases (5), Confirmation of these 
results was obtained by Peng (_7 ) , 

In summary, all investigators found 
that blink rates vary significantly 
across subjects. Some correlation exists 
between within-subject changes in blink 
rate and level of alertness. Further- 
more, blink timing and possibly the wave- 
form of the blink appear to be sensitive 
to task demands (9). 



PUPILLARY HIPPUS 



Changes in light intensity are known to 
produce alterations in the size of the 
pupil. It is less well known that pupil 
diameter can also be affected by internal 
factors such as interst value or task 
difficulty. Attentiveness to interesting 
material or the solution of difficult 
problems both were shown to lead to 
pupillary dilation (^)» Spontaneous 
changes in pupil diameter can also occur 
without visual input. Pupillary hippus 
is defined as the relatively slow change 
in the size of the pupil in the absence 
of external stimulation (10). Yoss 
demonstrated pupillary hippus to be 



associated with both states of drowsiness 
and a neurological condition known as 
narcolepsy (12-13). 

Previous experimental studies have in- 
dicated a correlation between inatten- 
tiveness or states of drowsiness or fa- 
tigue and the occurrence of various 
oculomotor activities and pupillary hip- 
pus. The relationships are not clearly 
defined or understood, but a good poten- 
tial appears to exist for utilizing these 
physiological factors as indicators of 
a mine equipment operator's state of 
alertness. 



LABORATORY INVESTIGATION 



The Bureau of Mines initiated a re- 
search program to define the predictive 
relationships between oculometric and 
pupillary phenomena and an individual's 
state of alertness. The study was con- 
ducted by Washington University, St, 
Louis, MO (10), Twenty subjects, all 
college-age adults, were selected from a 
pool generated by the Sleep Research Lab- 
oratory of St. Louis University. The 



test subjects participated in a vigilance 
testing program in which they were re- 
quired to respond to a series of simple 
visual and auditory stimuli. By examin- 
ing the accuracy of the responses, an 
indication of the subject's level of 
attention as a function of time on task 
was obtained. The test procedures for 
the visual and auditory vigilance testing 
are described in the following sections. 



36 



VISUAL 

The visual vigilance testing was self- 
paced with feedback, about erroneous re- 
sponses. The test utilized a stimulus- 
response unit, designed by Wilkinson 
( 11) , which presented the subject with a 
square array of four lights (fig. 1). An 
array of similarly arranged response but- 
tons was placed directly below the 
lights. The subject was instructed to 
pusph the button corresponding to the 
light in the array that was lit. As the 
subject depressed the button associated 
with a particular light, that light went 
off and another light came on. The posi- 
tion of the next light was randomly 
determined unless the subject responded 
incorrectly, in which case the light re- 
mained on until the correct response was 
made. Each subject performed this task 
for 10 min without interruption. 

AUDITORY 



duration was presented at 2-s intervals. 
The subject was instructed to simply dis- 
criminate between the tones and lift a 
finger from a response pad when the 200- 
ms tone was heard. Each subject per- 
formed this task for 32 min without 
interruption. 

TEST PROCEDURES AND INSTRUMENTATION 

Eyeblinks were monitored by placing Ag- 
AgCl electrodes in conjunction with dif- 
ferential amplifiers above and below the 
subject's right eye as shown in figure 2. 
Data were recorded on analog tape that 
was subsequently played into a computer 
for analysis. A program developed spe- 
cifically for the analysis of the eye 
movement data identified blinks and eval- 
uated their amplitude and closure dura- 
tion. An amplitude criterion that was 
fixed at 50 pet of total blink amplitude 
was applied to the data to identify 
closure duration. 



The auditory vigilance testing was 
paced by the experimenter without feed- 
back as to the accuracy of the 
responses, A tone of 200- or 300-ms 



Pupillary information was monitored by 
means of a closed-circuit television 
(CCTV) camera. During the vigilance 
testing, the subject was seated with his 




FIGURE 1, - Wilkinson stimulus-response unit. 



37 




FIGURE 2. - Ag-AgCI electrodes used to monitor vertical eye movements. 



or her head positioned in a restraint 
(fig. 3). The CCTV was aligned to ob- 
serve the pupil of the subject's left 
eye, and pupil size information was ob- 
tained from the television monitor. Mea- 
surements were taken over 1-min intervals 
at specified points in the testing pro- 
gram. The pupillometer was calibrated by 
positioning circles of known diameter in 
the head restrainst and adjusting the 
image on the monitor. All data were 
recorded on both strip charts and analog 
tape for subsequent data reduction. 

A typical example of the strip-charted 
data for the auditory vigilance testing 



is shown in figure 4. The lower channel 
depicts both the stimuli presentation and 
subject's response. As indicated on the 
figure, a downward deflection of the pen 
represents the presentation of the tone 
with the width of the square wave corres- 
ponding to the duration of the signal. 
The subject's response is displayed as an 
upward deflection of the pen. As can be 
seen in this example, the subject cor- 
rectly discerns the third signal as being 
200 ms in duration and responds appropri- 
ately. However, no response is recorded 
for the next signal, which is also 200 ms 
in duration. 



38 




FIGURE 3. - Head restraint and CCTV camera used to monitor pupil size. 



The middle channel recorded puplllo- 
metrlc information. Upward deflections 
are associated with pupillary constric- 
tions. The square waves seen in this 
plot are attributable to eyeblinks. True 
changes in pupil diameter are indicated 
by the gradually changing slope of the 
baseline. 

The upper channel recorded vertical eye 
movements such as blinks and closures. 
In the example shown, a long-duration 
closure occurs in the middle of four 
blinks. 



RESULTS 

Blink Rate 

The most apparent result from the 
study was that there was significant in- 
hibition of blinking during the visual 
vigilance testing. Figure 5 shows the 
blink rates exhibited during both visual 
and auditory vigilance testing and during 
a period of rest. It can be seen that 
the test subjects blinked more frequently 
during the rest period (17.0 bllnks/min) 
and auditory test (17.3 blinks/min) than 



39 



Vertical eye^ 
movement 



^r J/ui — njLL 



Response 
stimulus 



\ni 



M — ir~u~ 



FIGURE 4. - Sample strip chart from auditory vigilance testing. 



during the visual test (10.5 blinks/min) . 
No significant difference in blink rate 
was apparent between the rest period and 
the auditory test. As was expected, the 
performance of a task involving visual 
input led to a significant reduction in 
blink rate. Blink rate also tended to 
increase over time as the test pro- 
gressed, but these changes were not shown 
to be significant. 

Blink Closure Duration 

Blink closure duration, like blink 
rate, tended to increase as a function of 
time on task being performed. This 
trend, however, was not statistically 



significant. Figure 6 shows that closure 
duration, as expected, was longer during 
the auditory task than during gither the 
visual testing or the rest period when 
measured at 50 pet of full blink ampli- 
tude. There was no statistically sig- 
nificant difference between closure dura- 
tion for the visual testing and the rest 
period. Thus, it can be concluded that 
blink closure duration is significantly 
affected by the type of task subjects are 
called upon to perform, A visually de- 
manding task leads to a reduction in 
closure duration, while a task with no 
demands for visual processing leads to a 
significant increase in closure duration. 



40 



GO 



20 
I 8 
16 
14 
12 - 
I 

8 

6- 

4 

2 - 































:--S:\ 




o^\< 




x>-^^^ 






^^^<^ 


-^^^^ 






































^~^^\\ 




^-->>- 




L-^i».>~^ 



FIGURE 5. 



KEY 

■ At rest 

3 Visual vigilance testing (periods 1,2,3) 

^Auditory vigilance testing (periods 1,2,3) 

Eyeblink frequency data. 



Probably the most significant results 
were obtained by analyzing the eyeblink 
and closure data with regard to what was 
happening at the time the stimulus was 
presented. A special series of tests was 
conducted that required that the subjects 
respond to a 200-ms stimulus by lifting a 
finger from the response pad in the man- 
ner described previously. In these tests 
both auditory and visual stimuli were 
utilized. In the first test, the stimuli 
were presented at 2-s intervals, while in 
the second test, the interstimulus inter- 
val was varied from 0.8 to 3.2 s. 



A graphical representation of the re- 
sults is shown in figure 7. The plot 
presents the percentage of trials on 
which eyeblinks or closures occurred in 
association with either a correct re- 
sponse (hit) or a missed signal (miss). 
The results are discriminating in that, 
for both auditory and visual stim- 
uli, the incidence of blinks or closures 
associated with correct responses is 
markedly less than that associated with 
missed signals. These limited data indi- 
cate that when an eyeblink or closure 
was observed to have occurred during 



41 



0.16 

*^ .14 

z 

5 .12 



.10 
.08 
.06 
.041- 



^ .02 h 







mmim 












^^---' 


Vffy/yXfyK- 










III 




>^^'<~~ 
""\^^^ 










III 














liiiilii 






-^^^-- 




m^ 


iiiii 




^^^"-\ 




^^^^^' 






III 
















^\^^^ 




^x^"^^ 






WiM 








<^^^- 

^ 




^\^^^ 
--"\- 



KEY 

n At rest 

E Visual vigilance testing (periods 1,2,3) 

B Auditory vigilance testing (periods 1,2,3) 

FIGURE 6. - Eye closure duration data. 



presentation of an auditory stimulus, up 
to 60 pet of the time the signal was 
missed. Similarly, a visual stimulus was 
not responded to from 20 to 30 pet of the 
time. 

Relating this information to the orig- 
inal problem of operator alertness, it 
can be postulated that if information is 
presented to the operator by either 
visual or auditory means at the time an 
eyeblink or closure is occurring, between 
20 to 60 pet of the time the information 
will be missed and the operator will not 
make the required response. If the in- 
formation presented was critical to the 
safe operation of the vehicle, a good 
possibility exists for the occurrence of 
an accident. 

Blink Timing 

An analysis of the eyeblink data 
was also made to determine if any 



significance could be attached to the 
time that blinks occurred. As the inter- 
val between tones was fixed at 2 s in the 
auditory tasks, it was possible to eval- 
uate the time of blink occurrence during 
this interval. The first analysis con- 
sisted of dividing the interstimuli in- 
terval into two 1-s periods and evaluat- 
ing the number of blinks occurring in 
each period as a function of the perform- 
ance test responses. Responses were 
divided into four categories as follows: 

Hits — finger is lifted from response 
pad for 200-ms tone. 

False alarms — finger is lifted for 300- 
ms tone. 

Misses — finger is not lifted for 200-ms 
tone. 

No response hits — finger is not lifted 
for 300-ms tone. 



42 



60 



- 50h 

o 

a. 

< 

•- 30 

< 

^ 20 
10 







KEY 

■■Hits 
I I Misses 




Visual 
fixed 



Visual 
variable 



Auditory 
fixed 



Auditory 
variable 



FIGURE 7. - Percent of trials on which blinks and/or closures occurred during stimulus 
presentation. 



The data were analyzed for three sepa- 
rate 5-niin periods during the beginning, 
middle, and end of the auditory vigilance 
test. As can be seen from table 1, the 
number of blinks occurring in the first 
second immediately following stimulus 
termination is in excess of the 50 pet 
that would be expected to occur if blinks 
were distributed in a random manner. It 
can be concluded that, for most subjects, 
blinking was maximized during the period 
immediately following termination of the 
tone. This correlated well with previous 
studies cited earlier, which reported 
that blinks occurred at the moment of 
relaxation of attention following stimu- 
lus termination (5) and were inhibited 
prior to stimulus onset (_1_) . 

Pupillary Hippus 

Pupil diameter measurements were taken 
every 1.66 s over the 1-min monitoring 
intervals. Since the change in the pupil 



TABLE 1. - Mean percentage of blinks 
falling in first second of a 2-s 
interstimuli interval 



Test period and 
response 


Num- 
ber 1 


Mean 


Standard 
deviation 


Period 1: 

Hit 


17 
10 
13 

7 

17 

14 

8 

17 

17 

13 

5 

17 


67 
65 
82 
74 

74 
73 
75 
78 

72 
62 
65 
73 


24.5 


Miss ,- 


26.4 


False alarm 
No response 

Period 2: 
Hit 


hit. 


18.5 
14.0 

15.8 


Miss 


30.3 




26.7 


No response 

Period 3: 

Hit 

Miss 


hit. 


13.1 

19.5 
32.6 
41.8 


No response 


hit. 


15.8 



Sample population of 20. 



43 



diameter over time was the matter of con- 
cern. Von Neuman's d2 statistic was 
chosen to compare the data. The d2 sta- 
tistic is defined by the relation 



d2 = 



^ (X ,-X,^,)2 
n-1 



where Xj and Xj+] are successive pupil 
diameter measurements and n is the total 
number of measurements in the data set. 
It is commonly used to compare variations 
between successive samples and is there- 
fore a better measure for these data than 
the usual parametric measure of mean and 
standard deviation. 

During performance of the auditory vig- 
ilance test, pupil diameter measurements 
were made as described previously over 
four separate time periods. The time 



periods were 1 to 2, 9 to 10, 18 to 19, 
and 27 to 28 min for the 32-min test. 
Table 2 presents the results of the data 
analysis. It is readily apparent that no 
significant time on task effect is mani- 
fested. The distribution of d2 is widely 
variable, and contrary to the expectation 
that time on task effects would lead to 
an increase, no increasing trend is 
apparent. 

TABLE 2. - Von Neuman's d2 statistic dur- 
ing performance of the auditory vigi- 
lance task, sample population of 11 



Period 


Mean 


Standard 
deviation 


1 


2.85 
1.54 
2.18 
1.68 


2.83 


2 


1.33 


3 


3.39 


4 


1.45 



CONCLUSIONS 



Consistent with previous investiga- 
tions, the results from this study demon- 
strate the existence of significant task- 
related effects that influence eyeblink 
frequency rates. Performance of the 
visual vigilance testing resulted in a 
reduction in blink rate as compared with 
both a resting state and performance of 
the auditory vigilance testing. Although 
these results are far from conclusive, it 
can be hypothesized that during visual 
task performance a decrease in blink fre- 
quency rate is associated with the high- 
est level of alertness. 

The results of this experiment are more 
conclusive with respect to blink timing. 
The claim that blinks tend to occur when 
they interfere least with the processing 
of incoming information was supported. 
During the auditory task, blinks were 
reasonably tightly time-locked to stimu- 
lus termination. Clearly, this period 
occurs immediately after the most recent 
incoming information has been processed 
and farthest away from the expected pre- 
sentation of the next stimulus. Finally, 
it was discovered that blink closure 
durations are also sensitive to task 
demands. This is important in that 
blink closure does not exhibit as much 
between-subject variability as blink 
frequency does. It is therefore 



conceivable, given a clearer understand- 
ing of the correlation between degree of 
alertness and eye closure duration, to 
develop some universal monitoring cri- 
teria applicable to the majority of mine 
equipment operators. Perhaps the most 
important results concern the effect that 
oculomotor activity has on the reception 
of sensory stimuli. It has been shown 
that between 20 and 60 pet of visual and 
auditory stimuli were not responded to 
when eyeblinks or eye closures occurred 
dur-ing the presentation of the stimulus. 
This is important in that an operator's 
inability to respond appropriately to 
an unexpected situation accounts for a 
significant portion of mobile-mining- 
equipment-related accidents. 

The limited study undertaken concerning 
pupillary hippus revealed that the utili- 
zation of pupil diameter changes for 
identifying states of decreased alertness 
has more limited applicability than 
suggested by Yoss (12-13). Further 
investigation under conditions more 
closely following the previous studies of 
Yoss (12-13) and Lowenstein (6) would be 
required before any conclusive statements 
can be made. However, at the present 
time, pupillary changes seem to offer 
only limited po-tential as a real-time 
indicator of alertness. 



44 



REFEEIENCES 



1. Baumstimler, Y, , and J. Parrot, 
Stimulus Generalization and Spontaneous 
Blinking in Man Involved in a Voluntary 
Activity. J. Experimental Psychology, 
V. 88, 1971, pp. 95-102. 

2. Drew, G. C. Variations in Reflex 
Blink-Rate During Visual-Motor Tasks, 
Quar. J. Experimental Psychology, v. 4, 
1950, pp. 73-88. 

3. Hubert, S, T. Driver Alertness 
Monitoring System For Large Haulage Ve- 
hicles (contract HO282006, Tracer MBA), 
Final Rep,, November 1982, 118 pp.; 
available for consultation at Bureau of 
Mines, Twin Cities Research Center, Min- 
neapolis, MN. 

4. Janisse, M. P. Pupillometry: The 
Psychology of the Pupillary Response. 
Wiley, 1977, 204 pp. 

5. Kennard, D. S. , and G. H, Glaser. 
An Analysis of Eyelid Movements. J. Ner- 
vous and Mental Diseases, v. 139, 1964, 
pp. 31-48. 

6. Lowenstein, 0., R. Feinberg, and 
I, E, Loewenfeld. Pupillary Movements 
During Acute and Chronic Fatigue: A New 
Test for the Objective Evaluation of 
Tiredness. Investigation in Ophthalmol- 
ogy, V. 2, 1963, p. 138. 

7. Peng, D. L. , J. A. Stern, and L. N. 
Orchard. Chinese and American Readers: 
A Look at Information Processing Effi- 
ciency and Eye Movements. To be pub. 



in Pavlovian J, 
1983. 



Biolog. Sci, 



V. 18, 



8. Ponder, E., and W. P. Kennedy. 
On the Act of Blinking. Quart. J. Ex- 
perimental Psychology, v. 18, 1927, 
pp. 89-110. 

9. Sirevaag, E. J., J. A. Stern, 
P. J. Oster, and L. C. Walrath, The Re- 
lationship of the Eyeblink to Aspects of 
Performance, WA Univ, Behavior Res, Lab 
Rep., St. Louis, MO, 1982, 33 pp. 

10. Stern, J. A., and L. C. Walrath. 
A Study To Determine the Comparability of 
Pupillographic and Electrooculographic 
Measures in Determining Fatigue Effects 
in Truck Drivers (contract JO205064, WA 
Univ.). BuMines OFR 10-83, 1982, 65 pp. 

11. Wilkinson, R, T, , and D, Houghton. 
Portable Four-Choice Reaction Time Test 
With Magnetic Tape Memory. Behavior Res. 
Methods and Instrumentation, v. 7, 1975, 
pp. 441-446. 

12. Yoss, R, E,, N, J. Moyer, and 
R. W, Hollenhorst, Pupil Size and Spon- 
taneous Pupillary Waves Associated With 
Alertness, Drowsiness, and Sleep, Neu- 
rology, V, 20, 1970, pp, 545-554, 

13. Yoss, R, E,, N, J, Moyer, and 
K, N, Ogle. The Pupillogram and Narco- 
lepsy: A Method To Measure Decreased 
Levels of Wakefulness. Neurology, v. 19, 
1969, pp. 921-928. 



45 



LARGE ROPS AND OPERATOR RESTRAINT DEVICE RESEARCH 
By Stephen A, Swan"! 



ABSTRACT 



Rollover protective structures (ROPS) 
and seatbelts are required on all large 
self-propelled, track-type and wheeled 
mining equipment manufactured after 
July 1, 1969, used in mining operations. 
To keep a driver in thig protective 
structure in the event of a rollover, 
seatbelts are also required. 

Management and safety personnel realize 
the advantages of wearing seatbelts on 
ROPS-equipped machines; nevertheless, 
very few operators wear seatbelts. Some 



of the reasons why operators don't wear 
seatbelts follow: They are not comfort- 
able, they are not convenient to use, and 
the operator lacks knowledge of the ad- 
vantages of wearing seatbelts. 

This report delineates Bureau of Mines 
research to develop substantiated struc- 
tural design data for large ROPS (for use 
by the Society of Automotive Engineers) 
and the interrelated area of restraint 
technology. 



INTRODUCTION 



The Society of Automotive Engineers 
(SAE), through Subcommittee 12 — Machine 
Test Procedures of the Construction 
Machinery Technical Conunittee, develops 
rollover protective structure (ROPS) 
structural performance and test method 
criteria for use by industry in the de- 
sign and performance certification of 
ROPS used on a wide variety of mobile 
construction and mining machines. 

Certain types of mining, construction, 
earthmoving, agricultural, and forestry 
equipment are equipped with ROPS, The 
types of mobile machines commonly 
equipped with ROPS include crawler trac- 
tors and crawler loaders, motor graders, 
wheeled loaders and tractors, skid-steer 
loaders, and the tractor portion of 
tractor-scrapers. It is not uncommon to 
observe off-highway haulage trucks and 
water trucks that have ROPS installed. 

The widespread use of ROPS in the 
United States, Canada, and other coun- 
tries, is due to the relatively recent 
awareness of the extent of accidental 
rollovers of mobile equipment during 
field use. The development and implemen- 
tation of accident data collection and 

^Mining engineer. Twin Cities Research 
Center, Bureau of Mines, Minneapolis, MN. 



analysis activities by various Government 
and private groups has helped determine 
the numbers of injuries and deaths due to 
machine rollovers. Federal and State 
safety agencies have promulgated regula- 
tions requiring the installation of ROPS 
and seatbelts on these types of equipment 
in an attempt to reduce the number of 
injuries resulting from rollover acci- 
dents. Although these regulations 
require that the employer who owns the 
machine equip it with ROPS to provide a 
safer work environment for employees, 
most of the manufacturers of the machines 
are installing ROPS on the machines 
before they are shipped to their dealers. 

The ROPS regulations promulgated by the 
Occupational Safety and Health Admini- 
stration (OSHA) in 1972, by the Mine 
Safety and Health Administration (MSHA) 
in 1974 and 1977, by the State of Cali- 
fornia Division of Industrial Safety 
(Cal-DIS) in 1966, and by several of the 
Canadian Provinces base the ROPS struc- 
tural performance capability on criteria 
developed by SAE. It is recognized with- 
in the SAE technical committees respon- 
sible for developing ROPS performance 
criteria that these criteria need fre- 
quent update (every 5 yr) to introduce 
needed improvements. 



46 



The use of ROPS as required by the cur- 
rent law has saved many lives. A review 
of rollovers involving 56 machines with 
ROPS and 62 machines without ROPS indi- 
cated over four times as many fatalities 
involving machines without ROPS. In 
addition, ROPS-equipped machines in many 
rollovers have prevented injuries, and 
therefore these events have never been 
reported. In addition indications are 
that none of the operators killed in 
rollovers of ROPS-equipped machines were 
wearing seatbelts. If the operators of 
the ROPS-equipped machines had used 
seatbelts, all of them might have sur- 
vived the rollover. 



quite different from those in automotive 
applications. Although the trend is 
toward enclosed cabs, many pieces of 
equipment do not have cabs, or the cab 
doors and windows are kept open most of 
the time. Consequently, a seatbelt 
assembly installed on surface mining 
equipment must be capable of performing 
satisfactorily during and after prolonged 
exposure to the elements of the mine 
environment. In addition to the direct 
outdoor exposure, the seatbelt assembly 
may come into contact with hydraulic oil, 
fuel, dust, and other operational ele- 
ments that can rapidly deteriorate its 
effectiveness. 



Seatbelts installed on surface mining 
equipment are subjected to conditions 



ROPS PERFORMANCE 



The objective of the Bureau of Mines 
ROPS work was to determine, within the 
limitations of the data available, 
whether or not ROPS are providing ade- 
quate protection to the operators of 
mining equipment. As part of Bureau 
contract JO285022, "Survey of Rollover 
Protective Structures (ROPS) Field Per- 
formance," conducted by Woodward Asso- 
ciates, Inc., the following results were 
obtained: 

1. ROPS do the job for which they are 
intended. There has been a significant 
reduction in deaths due to mining and 
construction machine rollovers, as shown 
in table 1 for earthmoving equipment. 



2. Many ROPS designs currently in use 
on equipment in the field have structural 
performance capabilities that signifi- 
cantly exceed the requirements given in 
SAE recommended practices. 2 This in- 
dustry practice may have a positive in- 
fluence on the excellent lifesaving rec- 
ord of ROPS. 

^SAE recommended practice Jl040(c), 
"Performance Criteria for Rollover Pro- 
tective Structures (ROPS) for Construc- 
tion, Earthmoving, Forestry, and Mining 
Machines," is available from Society of 
Automotive Engineers, Warrendale, PA. 



TABLE 1 



ROPS effectiveness in earthmoving equipment rollovers, percent 





Machines equipped 

with ROPS 

(102 accidents) 


Machines not 

equipped with ROPS 

(101 accidents) 


Machines with 
ROPS status un- 
known (28 accidents) 


No injury, 


37.3 
25.5 
18.6 
14.7 
3.9 


13.9 
13.9 
21.8 
48.5 
1.9 


35.7 




10.7 




14.3 


Fatality..,,,.,. 


21.4 


Unknown. 


17.9 


Total 


100.0 


100.0 


100.0 



47 



3. This study was unable to confirm 
the adequacy of the structural perform- 
ance criteria presented in SAE recom- 
mended practices. The ROPS that have 
saved lives in the mining and construc- 
tion industries significantly exceed the 
minimum SAE requirements. It is possible 
that ROPS designed simply to meet the SAE 
recommended practices would provide less 
satisfactory operator protection. 

4. If machine operators can be per- 
suaded to wear their seatbelts and stay 
with the ROPS-equipped machine, their 
chances of surviving a rollover are many 
times greater than if they attempt to 



jump or if they are thrown from the 
machine, 

5. Different generic types of machines 
have been shown to experience different 
severities of rollover. There is a dif- 
ferent "typical" or "standard" rollover 
for each type of machine and perhaps even 
some differences within some generic 
types. Therefore the ROPS performance 
criteria should be based on protecting 
the machine operator in a high percentage 
(say 95 pet) of the possible rollover 
accidents for each generic class of 
machine. 



LARGE ROPS ROLL TESTING 



The SAE ROPS criteria were developed by 
building ROPS, performing side and top- 
load tests on the ROPS when installed on 
the vehicle, and then rolling the vehicle 
equipped with the ROPS down a test hill. 
In the late 1960's, when these criteria 
were being developed, the largest ma- 
chines were in the 140,000-lb range. As 
the machines became bigger, the SAE cri- 
teria were extended to cover these ma- 
chines, but no actual roll tests were 
conducted. 

The required energy curve representing 
force versus machine gross vehicle weight 
(GVW) was flattened as the machines be- 
came larger, since the operator's com- 
partment became much smaller in relation 
to the size of the machine. Thus, de- 
signers projected that other parts of the 
machine, in addition to the ROPS, would 
absorb energy and provide protection. 



survived rollover on a similar slope. 
The manufacturer redesigned the ROPS for 
both machines, exceeding SAEJ394 and 
SAEJ395 "small machine" ROPS performance 
criteria. Both machine ROPS then sur- 
vived rollover testing. 

These rollover tests have provided 
the first available test data on a 
large machine rollover. The tests have 
raised the serious question as to what 
criteria should be used for large 
(200,000 lb) machines and particularly 
very large (350,000 lb) machines. It 
must be remembered that these test data 
were the only information available at 
the time the Bureau's ROPS program was 
started and the conclusions drawn from 
these tests may be relevant only to the 
particular model and configuration of 
front-end loader and crawler tractor 
involved. 



In late 1977, a machine manufacturer 
performed rollover tests of a large 
wheeled loader and a large crawler trac- 
tor weighing approximately 200,000 lb. 
Original ROPS designs for both machines 
exceeded SAE J1040(b) performance cri- 
teria. The wheeled loader ROPS fractured 
and was essentially crushed by a 180° 
side roll down a slope. The crawler ROPS 



The Bureau obtained two large front-end 
loaders (FEL) (390,000 and 286,000 lb) 
from equipment manufacturers to provide 
data by actual rollover tests. On the 
recommendations of the original equipment 
manufacturers, the following were se- 
lected for testing under Bureau contract 
HO2902020, "Development of ROPS Perform- 
ance Criteria For Large Mobile Mining 



48 



Equipment," with Woodward Associates, 
Inc. : 

1. Roll hill slope of 35°. 



combined ROPS-machine configuration were 
factors that caused lower than expected 
side loads, a conf igurational parametric 
study was undertaken. 



2. Roll hill length of 120 ft (to 
enable the largest machine to roll a max- 
imum of 720°). 

3. A penetration resistance of 1,800° 
psi for the roll hill. 

All ROPS structures were instrumented 
to record 20 channels of strain, 6 chan- 
nels of deflection, 3 channels of accel- 
eration, 2 channels of roll rate, and 4 
time channels. Three roll tests were 
conducted: 



A computer simulation of a rollover is 
being conducted using the ROPS impact 
instrumentation data obtained during the 
rollover testing. The following config- 
urational parameters are being evaluated 
in respect to the gross vehicle weight 
(GVW) to determine ROPS performance: 

1. Width of ROPS. 

2. Width of machine (including tires). 

3. Length of ROPS (at top). 



a. First roll test (720°) for a 
390,000-lb FEL (fig. 1). 



4. Plan-view area of the ROPS top 
plate. 



b. Second roll test (720°) of 
390,000-lb FEL (fig. 2). 



5. Area of ROPS viewed from the side 
(with cab if integral to ROPS). 



c. Roll test (720°) of a 286,000-lb 
FEL (fig. 3). 



6. Area of ROPS longitudinal cross 
members viewed from the side. 



A factor that most significantly 
affects the loading on a ROPS dur- 
ing rollover is the overall ROPS-machine 
configuration as demonstrated during 
the third test using a 286,000-lb FEL. 
Since the ROPS configuration and/or the 



Available roll data are being obtained 
from the original equipment manufacturer. 
This project, which is nearing comple- 
tion, will result in an updated SAE rec- 
ommended practice for ROPS performance 
criteria. 



OPERATOR RESTRAINT TECHNOLOGY 



Once the protective structure around a 
driver is assured, in the event of a 
rollover, the need exists to increase the 
number of operators of surface mining 
equipment using restraint devices, such 
as seatbelts, that keep them inside the 
structural protection. Although ROPS and 
seatbelts are required on all mobile min- 
ing equipment, injuries are still occur- 
ring to operators who do not use the 
seatbelts for containment within the pro- 
tective area of the ROPS during rollover. 
The three most common complaints regis- 
tered by operators about seatbelts were 
fit, comfort, and convenience. Therefore 
these aspects of the restraint system 
were first addressed and analyzed. To 



satisfy these criteria and retain the 
operator safely in the seat in the event 
of vehicle rollover, two new design con- 
cepts were developed. The first design 
uses a vehicle-sensitive retractor (VSR) 
which relies on a counterweight to acti- 
vate the belt locking mechanism any time 
the gravitational forces displace the 
counterweight owing to vehicle attitude 
or acceleration-deceleration forces. The 
automotive VSR mechanism operates at 
approximately 0.3 g. For off-road vehic- 
les it was adjusted to operate at 0.75 g. 
Simulated rough terrain tests and roll- 
over tests indicated that this should be 
both a safe and an acceptable activation 
level. 



49 




% 







'''^W^%^,'^%[ 






^-^^1 






WEIGHT COMPARISON 
PICKUP TRUCK 4,500 ib 
DC-IO JETLINER 244,193 tb 
WHEELED LOADER 390,000 lb 






50 





'"^V^I^'ll^KK CM 










51 











52 



To evaluate this design, a seatbelt 
rollover test was conducted in conjunc- 
tion with the ROPS rollover program, uti- 
lizing a 50th percentile anthropomorphic 
male dummy weighing 160 lb. Seatbelt 
loads were obtained for both the left and 
right sides of the belt. With the excep- 
tion of the longitudinal head accelera- 
tion, these values were obtained during 
the first impact of the ROPS. The verti- 
cal acceleration of the dummy's head ex- 
ceeded the limitation of the acceler- 
ometer, which was approximately 20 g. 
The maximum longitudinal head accelera- 
tion occurred after the first impact. 

The average seatbelt load was approxi- 
mately 5.7 times the weight of the dummy. 
This load level is not as high as might 
be expected from the head acceleration 
rates. This difference may be due to the 
fact that the acceleration rate and the 
roll direction of the machine must be 
considered in comparing the dummy head 
accelerations with the seatbelt loading. 
Maximum seatbelt loads along with maximum 
dummy head acceleration rates are shown 
in table 2. 

The major advantages of the VSR system 
over present lapbelt systems were as 
follows: 



1. The VSR belts provided mobility for 
the operator to make the necessary move- 
ments for vehicle operation, remained in 
an unlocked condition most of the time, 
and locked when extremes of terrain were 
encountered. 

2. Tests indicate the belt assembly 
would also lock in a rollover condition 
as designed. 

3. Operator acceptance of the seatbelt 
was enhanced by the improvement in com- 
fort and fit. 

4. The cleanliness aspect was greatly 
improved since the belts retracted for 
storage, 

TABLE 2. - Maximum seatbelt loads and 
head acceleration 



Parameter 



Seatbelt load — left sfde... 
Seatbelt load — right side.. 

Average seatbelt load 

Vertical acceleration 

Side acceleration 

Longitudinal acceleration, . 



lb. 
lb. 
lb. 
.g. 
.g. 
.g. 



Maximum 
value 

816 
1,013 

914 
20.7 
8.14 
2.83 



VEST RESTRAINT SYSTEM 



Recognizing that there are some prob- 
lems associated with lapbelt-type re- 
straining systems, namely the fear of 
entrapment, the restriction of movement, 
and the lack of comfort, the Bureau de- 
veloped a second design concept creating 
a novel restraint system. The essentials 
of this system are a vest restraint sys- 
tem (VRS) phown in figure 4 and a teth- 
ered line or retractor-type anchoring 
device. 



retractor, use snaphooks 
the vest D-rings. 



to connect to 



The combination of a VRS and an anchor- 
ing device should eliminate most of the 
problems encountered with lapbelts. 
Also, the VRS would become part of the 
operator's personal safety gear, thereby 
encouraging the use of the restraint sys- 
tems more than do soiled or inoperative 
lapbelts. 



The VRS has an upper-body harness in- 
corporated in the vest structure to give 
upper torso restraint in the event of 
vehicle rollover. This harness is made 
with standard 2-in seatbelt webbing and 
in-line adjusters. A quick-release 
safety buckle secures the vest and 
harness about the waist. D-rings sewn 
onto the vest webbing are the connection 
points for the anchoring device. The 
anchors, whether fixed-length tether or 



A preliminary analysis of the VRS indi- 
cates that the prototype vest can be com- 
fortably and easily adjusted for proper 



fit. Because of 
attachment devices for 
buckets on the VRS, the 
can be free during 
from the equipment. 



snaphooks and other 
tools and lunch 
operator's hands 
ingress and egress 
This improved way of 
carrying items aboard the vehicle will 
reduce slip and fall accidents. 



53 




FIGURE 4. - Vest restraint system. 



54 



CONCLUSIONS 



ROPS and seatbelts are designed and 
installed on surface mining equipment to 
protect the operator in the event of 
machine overturn. The two systems depend 
on each other for proper protection for 
the machine operator. Accident data 
analysis shows that ROPS do perform the 
function for which they are intended, and 
that there has been a significant reduc- 
tion in deaths due to mining and con- 
struction machine rollover since ROPS 
have been required. Preliminary data 
from the large ROPS roll testing indicate 
that large front-end loaders have differ- 
ent roll characteristics than smaller 
machines. These characteristics and the 
test data are being evaluated by the 
Bureau and private industry. Owing to 
Bureau efforts, ROPS performance require- 
ments for the first time will be based on 
rigorous engineering analysis of actual 
rollover data. Therefore the new SAE 
recommended practice developed from the 
information obtained by this project will 
have a sound engineering basis that will 
also provide operators of ROPS-equipped 
machines wearing seatbelts better protec- 
tion in the event of rollover. 



Despite company policies requiring that 
operators wear belts, present use of 
seatbelts is very low. Only 5 pet of the 
accident reports even mentioned whether 
seatbelts were worn or not. The rest of 
the forms were left blank. Only 2 pet of 
all the accident reports stated that 
seatbelts were worn. Therefore a new 
restraint system is warranted, based upon 
present lack of usage and the need for 
increased protection. 

A preliminary subjective analysis of 
available restraint technology indicated 
that seatbelts must be comfortable and 
easily adjusted. A vehicle-sensitive 
retractor (VSR) seatbelt system was 
developed to provide improved comfort, 
fit, and convenience. The VSR system 
also provides manual locking capability. 
A second alternative is provided by a 
vest restraint system (VRS) that is 
issued to the operator as personal equip- 
ment. This system incorporates several 
attractive safety features that will 
encourage the person to keep it clean and 
well maintained and should therefore 
receive more use. 



55 



OFF-HIGHWAY HAULAGE TRUCK MAINTENANCE SAFETY 
By Dennis A. Long1 



ABSTRACT 



This paper assesses the haulage truck 
maintenance safety problem and reports in 
detail maintenance accident data for 
recent years. Further analysis quanti- 
fies the safety hazard in terms of job 
activities, truck components and systems, 
tools involved, and truck design. 



Together with practical information 
obtained from industry experts, recom- 
mendations are presented to enable the 
mining industry to make changes where 
specifically needed to abate the increas- 
ing safety hazard to truck maintenance 
mechanics. 



TRUCK MAINTENANCE PERSONNEL 



Workers below the age of 31 were in- 
volved in 49.0 pet of all truck mainten- 
ance accidents. Workers with less than 
6 months* experience in the particular 
job held at the time of the accident 
accounted for 27 pet of all accidents; 
and 59.0 pet had less than 3 years of 
job experience. Figure 1 gives the 
percentage of truck-maintenance-related 
accidents by job title. Maintenance per- 
sonnel, including mechanics, helpers, and 
trainees, accounted for 65.0 pet of the 
accidents, while the mine equipment oper- 
ators accounted for over 25 pet. 

To examine the nature of the injuries, 
the Bureau classified the severity of 
haulage truck maintenance accidents by 
work days lost (table 1). Most mainten- 
ance accidents were not characterized by 
severe injuries, as 33.5 pet of the acci- 
dents involved no lost time and 41.3 pet 
involved between 1 and 15 lost days. 
Information from mine visits indicates 
that maintenance also accounts for a 
large number of unreported accidents. 

The body parts injured in maintenance 
accidents are presented in figure 2, with 
the data grouped into major categories. 
Head and neck injuries accounted for 16.2 
pet, and major body injuries, involving 
the chest, back, hip, or trunk, to- 
taled 33.5 pet. Back injuries involved 
16.1 pet and eye injuries 7.0 pet. 

^Mining engineer. Twin Cities Research 
Center, Bureau of Mines, Minneapolis, MN. 



Maintenance injuries commonly involve the 
extremities, accounting for over one- 
half of all accidents. This includes 
hand (22.5 pet), leg (10.1 pet), and foot 
(7.3 pet). 

TABLE 1. - Truck maintenance accidents by 
lost work days, U.S. surface mines, 
1978-79, percent 

33.5 

1 to 5 19.6 

5 to 15 21.7 

15 to 30 8.9 

30 to 60 10.1 

Over 60 6.2 

Total 100. 

Injuries most commonly resulted due to 
lack of proper training for the particu- 
lar job being done at the time of the 
accident. Unsafe actions accounted for 
71.5 pet of all accidents. This category 
includes taking an unsafe position, using 
equipment unsafely, nullifying safety 
devices, failing to use a platform or 
personal protection, and horseplay. 
About 41 pet of all accidents were due to 
the worker's taking an unsafe positon, 
such as reaching beyond the lifting ra- 
dius or attempting to climb a ladder with 
a heavy part in hand. Failure to secure 
caused 19.0 pet and included causes such 
as improper support of heavy parts and 
components or failure to secure the truck 
box. 



56 



Mechanic helpers or trainees 3.0 pet 



Electricians 2.1 pet 



Welders 4.3 pet 



Supervision 2.1 pet 




FIGURE 1. - Truck maintenance accidents by job title. 



Because of the significant number of 
accidents due to unsafe actions taken by 
the ti?-uck mechanic, it is likely that a 
key safety problem is the lack of effec- 
tive skill training. Further examination 
of the problem reveals that the mainten- 
ance people were commonly — 

1. Performing tasks for which they 
were not formally or adequately trained. 
This includes both equipment operators 
doing maintenance-type work and mainten- 
ance mechanics tramming a piece of equip- 
ment to and from the shop. Over one- 
fourth of all haulage truck maintenance 
accidents involved equipment operators. 



2. Not following prescribed procedures 
or safety precautions. This would in- 
clude disregarding lockout procedures or 
nullifying a safety device. 

3. Working with inadequate or impro- 
vised tools and equipment. Although the 
mechanic may be taking an unsafe action, 
there may not be any other way to get the 
job done. 

Most maintenance training in the mines 
consists of safe work briefings followed 
by on-the-job experience under either a 
lead mechanic or a senior employee. 
Instruction varies and is based on the 



57 



Head and neck 16.2 pet 



Upper extremities 
32.9 pet 



Lower extremities 
17.4 pet 




FIGURE 2. - Truck maintenance accidents by 
body part injured. 



The second most frequently identified 
training need was for guidebooks for spe- 
cific maintenance tasks, such as a manual 
on the haulage truck electrical system, 
cooling system, hydraulics, or electronic 
components. Again, several manufacturers 
have materials that can be purchased, but 
they cover only a limited number of main- 
tenance tasks on a specific truck model. 
Some manufacturers have no effective 
manuals for their products. The follow- 
ing areas were identified by maintenance 
personnel for improvements in maintenance 
manuals: 

1. Must be specific, complete, and up 
to date. Numerous manufacturers try to 
use one manual for all makes and models. 
This makes manuals complex and lengthy. 
Older models are dropped and new ones 
added without updating the manuals. 

2. Must have a good cross-reference 
and index system. 



teaching skills of the supervisor. Ex- 
perience is not necessarily the best 
teacher. Emphasis should be placed on 
recognizing specific hazards, knowledge 
of proper job procedures for the various 
truck models and systems, and correct use 
of tools and equipment. 

Proper job procedures and tool use 
could be enhanced through easy-to-use 
troubleshooting guides. Fewer than half 
of the equipment manufacturers provide 
such guides for their products. Most of 
the available guides need to be improved 
substantially in terms of both effective- 
ness and ease of use. Only four major 
manufacturers were frequently praised for 
providing good to excellent troubleshoot- 
ing guides. 



3. Should include 
troubleshooting guide. 



an effective 



4. Should provide updating capability 
so that technical corrections, improved 
maintenance procedures, and safety warn- 
ings can be brought to the attention of 
site personnel, 

5. Should be compact and easily port- 
able for use in working sections. 

Mechanics should also be trained and 
qualified to operate the equipment they 
maintain. Although their job involves 
shuttling equipment in the shop area, 
mechanics are typically not trained to 
operate the machines and are not familiar 
with their safe operating limits. 



TRUCK MAINTENANCE SHOPS AND AREAS 



As expected, most accidents occur in 
the shop, where the maintenance usually 
takes place. Specifically, 70.7 pet of 
all haulage truck maintenance accidents 
occurred in the shop. The importance of 
accident location increases when it 
is considered that most maintenance ac- 
tivities take place within the shop 



facilities. Although 29 pet of the acci- 
dents studied occurred in the field, it 
is estimated that only about 10 to 15 pet 
of the maintenance work was done there. 
Thus, field maintenance work is two 
to three times more hazardous as shop 
work. 



58 



An important recommendation, to counter 
the hazards of field maintenance work, is 
to develop and use towing vehicles cap- 
able of moving disabled trucks to the 
shop. Towing a large haulage truck is 
very difficult, involving two or more 
support vehicles and additional person- 
nel. But because of the high capital 
cost, only a few of the largest mining 
operations in the United States have spe- 
cialized towing vehicles. Another solu- 
tion might be to retrofit the truck so 
that it can be towed more easily. 

Improved physical design of maintenance 
areas and equipment bays could help re- 
duce accidents. Included here would be 
such factors as work space organization, 
housekeeping, illumination, ventilation, 
noise control, and transporting of parts. 
An effectively designed workspace could 
enhance productivity, allow more effi- 
cient use of tools, and improve safety. 
Roughly 30 pct of the accidents involved 
poor housekeeping practices. 

Poor workspace organization was common 
in most of the mines visited, manifested 
as follows: 

1. Handtools and small powertools 
strewn about or stored wherever space 
permitted, forcing people to climb over 
or reach around them. 

2. Tools or parts not conveniently 
located, requiring people to search for 
them. 



4. The work performed on oil- or 
grease-splattered ground or in the field 
on unimproved rocky ground. 

Because most truck maintenance shops 
must service larger trucks than they were 
originally designed for, there is often 
insufficient space between truck bays to 
use tire grabbers for forklifts. 

Another important truck shop problem 
is communication. Large mining ma- 
chines frequently have two or more people 
working on or around them at any time. 
It is important that these people be able 
to communicate their intentions and ac- 
tions to each other. Numerous accidents 
have involved communications breakdowns. 
Inexpensive technology is available to 
resolve many of those problems. Simple 
solutions could include lockout equipment 
or proper tagging of trucks being worked 
on. 

Because of the high incidence of 
handtool-related injuries, it is also 
recommended that emphasis be placed 
on tool maintenance. Mobile racks should 
be developed for special tools, since 
mechanics often improvise a tool set- 
up when the proper tool cannot be found. 
Dealers or distributors should be encour- 
aged to stock proper tools. Often the 
tools are manufactured but are unavail- 
able from the local distributor. Thus, 
the mine shop is forced to design and 
fabricate something on the spur of the 
moment. 



3. Shop floors covered with cables and 
hoses, presenting a tripping hazard. 

TRUCK DESIGN FOR SERVICEABILITY 



Some problems are caused by the poor 
design of the truck for routine or major 
maintenance. Design improvements would 
substantially reduce maintenance time and 
maintenance-related injuries. 

The following are a few examples to 
illustrate the need for maintenance 
safety preplanning for large off -highway 
haulage trucks. On one 120-ton- 
capacity, electric-drive, rear-dump 
truck, the changing of a wheel motor 
was particularly time consuming and 



hazardous. To remove the motor, it was 
necessary to remove the truck bed, the 
entire rear axle assembly, and the casing 
around the axle-wheel assembly to expose 
the broken unit. After the motor was 
removed and a new unit installed, the 
procedure was reversed for reassembly. 
Mine maintenance people suggest that this 
task could be easily performed and with 
much improved safety if access openings 
had been provided through the motor-axle 
housing. 



59 



Another example involved a 120-t on- 
capacity, bottom-dump truck. To change 
fan belts or certain hoses, either the 
radiator or the engine block had to be 
removed. Several minor injuries had been 
associated with this work. On certain 
larger trucks, personnel must crawl in- 
side the rear axle housing to adjust the 
service brakes. Other examples of poor 
design related to routine maintenance 
were also identified. For example, minor 
slip and fall accidents result when 
people mount large trucks to fuel them. 
This hazard increases in rain, snow, or 
icy weather. Likewise, inspections of 
engine fluid levels and critical hy- 
draulic hoses, and similar checks, are 
often difficult and hazardous to perform. 
The machine surfaces crawled on or over 
are typically coated with grease and are 
slippery. 

By combining the truck maintenance 
accident data with field-gathered main- 
tenance worktime, it was concluded that 
the most hazardous components to work on 
are the tires and wheels, truck body, 
suspension, and engine. The least haz- 
ardous components are brakes and drive 
train. Overall there is a direct corre- 
lation between accidents and the size and 
scale of the component or part to be 
worked on. Through analysis of the acci- 
dents and mine surveys, a number of 
design problems relevant to truck main- 
tenance were identified: 

1. Poor accessibility to machine parts 
or areas of the unit for routine or un- 
scheduled maintenance tasks. 

2. Inadequate access openings to per- 
mit a person to reach or climb in for 
repairs or to replace parts. 

3. The need to remove or dismantle 
ancillary components in order to access 
the failed unit. 

4. Inadequate or no provisions for the 
safe handling of heavy or large parts. 

5. Inadequate tools to perform the re- 
quired maintenance task. 



6. The need to perform many repairs on 
the spot without the resources typically 
available in the shop area. 

Because of the large size of many ma- 
chines, these items interact to make 
field maintenance both difficult and 
hazardous. 

In some cases, specific equipment modi- 
fications would help alleviate hazards. 
Usually, the changes would involve orig- 
inal equipment options to be offered by 
the truck manufacturers. However, new 
options that would enhance truck mainten- 
ance safety are often ignored, since the 
mine's safety department rarely influ- 
ences truck purchasing decisions. 

Improved truck design should be matched 
with redesign of components, procedures, 
tools, and manuals. The main design 
faults include the following: 

1. Designing machines that require 
unskilled-to-skilled mechanics to perform 
complex sequences of tasks in order to 
keep equipment operational. 

2. Requiring mechanics to manipulate 
large, heavy vehicle components in tight 
spaces with inadequate clearances, sup- 
ports, and tools. 

3. Designing equipment such that ac- 
cessibility for routine maintenance tasks 
is overly complex, such as having to re- 
move a large radiator in order to change 
a fan belt. 

4. Providing inadequate access open- 
ings, clearances, and visibility for 
tasks to be performed. 

A side-by-side comparison of older mo- 
bile mining equipment with newer models 
indicates that although changes in truck 
design have occurred, the majority of 
changes have related either to the equip- 
ment operator's safety and comfort or to 
the production features of the truck. 
Much work remains to be done in the area 
of maintenance safety. 



60 



TRUCK MAINTENANCE JOB PROCEDURES 



Further analysis of the data deter- 
mined the frequencies for the various 
causes of maintenance accidents. Table 
2 lists accidents by activity of the 
injured. These generic activity de- 
scriptions were created to simplify 
the data analysis. Movement around the 
shop area and up and down the mobile 
equipment accounted for about one- 
fourth of the injuries. This number re- 
flects the need for adequate work plat- 
forms, access steps, ladders, and good 
housekeeping. 

TABLE 2. - Truck maintenance accidents, 
by activity of the injured, U.S. sur- 
face mines, 1978-79, percent 

Installing part 23.2 

Removing part 18.3 

Servicing equipment 16.2 

Inspection 15.2 

Getting on and off equipment 14.9 

Movement around shop area 10.1 

Cleaning 2. 1 

Total 100.0 

The job factors that contribute most to 
injuries include — 

1. Lack of knowledge about correct 
material handling practices. 



would have been reduced or eliminated 
with gloves, 

6. Lack of supervision. 

Removing and replacing parts accounted 
for 41,5 pet of all accidents studied. 
Frequently, the weight of a part was 
taken on by the injured person at too 
great a distance from the body, resulting 
in strains, sprains, or crushed or lacer- 
ated fingers when it dropped. In most 
cases, removal and replacement of parts 
involves support equipment, but wire rope 
slings and chains tend to slip when they 
lift items by choking around them. A 
sudden movement can cause the sling to 
lose its grip and cause the part to fall 
free. 

It is recommended that maintenance per- 
sonnel be encouraged to use proper lift- 
ing equipment, or to add people for hand- 
ling heavy parts and equipment, such as 
drivetrain, tires, and suspension. Im- 
proved job training and employee aware- 
ness of the weights and necessary hand- 
ling equipment for different components 
and parts would help. Also, the manu- 
facturers should emphasize possible haz- 
ards in manuals and through warning 
stickers placed on the equipment. 



2. Limited aids for material handling 
such as lifting devices, jacks, and 
hoists, 

3, Lack of effective training programs 
and wprk procedures for manual material 
handling, typified by the prevailing at- 
titude that back injuries due to lifting 
"will not happen to me," 

4, Inadequate workstands or platforms 
for support during tasks requiring reach- 
ing or lifting. 

5. Inadequate use of personal protec- 
tion equipment such as gloves, lifelines, 
or other protective devices. Over 21 pet 
of the injuries to the hands or fingers 



Fifteen percent of the accidents stud- 
ied involved a fall from the truck frame, 
bumper, platform, or tire, owing to inad- 
equate access or workstand. Portable 
stands are used widely in the industry, 
but they are usually designed for a par- 
ticular maintenance task, such as chang- 
ing oil filters. If a stand is used for 
another task, such as working on the 
starter, it may be either too high or too 
low. This places the mechanic in a 
difficult position and increases fatigue 
and the possibility of an accident. A 
single stand with adjustable height 
could take the place of several stands. 
Such a stand could be modeled after the 
racks used to drop differentials or 
transmissions. 



61 



Table 3 summarizes haulage truck main- 
tenance accidents by their source, or the 
item that directly caused the injury. 
This information reveals that the truck 
body and/or large components directly 
inflicted about a third of the injuries. 
The work station, including makeshift 
supports, ladders, workstands, or the 
shop floor, was the source for 31.0 pet 
of the accidents. 



moving the tireman away from tires. Some 
companies have contracted outside sources 
for tire maintenance. 

A review of tire maintenance practices 
indicates the following: 

1. Protective screens are necessary 
for people working on or around large 
tires. 



TABLE 3. - Truck maintenance accidents, 
by source of injury, U.S- surface 
mines, 1978-79, percent 

Truck body and/or large components 32.5 

Work station 31.0 

Tools and equipment 9.6 

Shop area hazards 9.6 

Truck parts 8.0 

Tires, wheels, hubs, or rims 5.9 

Heat or flame 3.4 

Total 100.0 



2. Tools used to mount and dismount 
tires are inadequately designed and re- 
quire much physical exertion. 

3. The lifting devices, such as modi- 
fied forklifts, are inadequate in design 
and in their degree of control over the 
tire and wheel. 

4. Inappropriate tools and unsafe 
equipment are used in the absence of 
proper tools. 



The truck body or large components 
accounted for about one-third of all 
accidents. Two fatalities occurred in 
1980 as a result of failure to secure the 
truck box during maintenance. In addi- 
tion, numerous near-misses and many in- 
juries occurred near medium-size end- 
dump doors or tailgates. It is recom- 
mended that a definite means of securing 
truck boxes or tailgates be employed and 
that locking pins or similar devices be 
provided under the bed. One mine visited 
has fabricated a hook-and-eye system that 
is permanently installed on the truck. 

One of the most hazardous maintenance 
tasks is the removal, repair, and re- 
placement of large tires. In reviewing 
accident reports, it became obvious that 
procedures for de-airing, airing, remov- 
ing, and replacing tires are inadequate. 
In about 12 pet of accidents studied, 
mechanics were injured when hit by pry- 
bars or wedge clamps, or by retaining 
rings damaged during previous repairs. 
Many mines have purchased tire-grabbing 
equipment, which aids in removal or 
replacement of tires, improving safety by 



5. Lack of an effective tire damage 
and wear guide mades it difficult to es- 
timate the risk of tire explosions. 

6. Inappropriate work practices or 
procedures are followed when working with 
high-risk tires. Sometimes tires are 
brought into the shop rather than to a 
designated remote area. 

7. Often, little or no formal train- 
ing is provided to tire maintenance 
personnel. 

These and other factors contribute to 
the high risk associated with working 
with large tires. A number of steps have 
been taken by various mines to minimize 
these hazards. For example, 

1. Many mines fabricate a special 
"cage" to protect against blowups during 
inflation and deflation. 

2. One tire foreman devised a tire- 
mounting tool and had a local machine 
shop fabricate it. That shop now sells 
the unit to other mines in the area. 



62 



3, Many mines have constructed spe- 
cial, protected areas, where all tire 
work is completed. Should an explosion 
occur, workers in adjacent areas would be 
protected. 

Over the 2-yr period (1978-79), tools 
and equipment were involved in about 10 
pet of the total accidents. Table 4 
lists accidents by tools and equipment. 
Handtools accounted for almost one-third 
of all injuries. Elevated platforms and 
servicing equipment such as jumper cables 
and airhoses were each involved in 15 pet 
of the accidents. 

Maintenance of off-highway trucks is 
complex and specialized, and usually 
must be completed outside the realm of 
conventional hand and small power 
tools. Therefore, the design of spe- 
cial handtools could substantially 
improve maintenance safety. Without 
knowledge about or availability of spe- 
cially designed tools, shop personnel 
often resort to unsafe practices and 
procedures, locally designed and/or 



fabricated tools, and misuse of available 
tools. 

The most important recommendation re- 
garding handtools is for supervisors to 
take more responsibility for insuring 
that the right tools are used for the 
right job. Also, the importance of tool 
availability, maintenance, and proper 
storage is again emphasized. 

TABLE 4. - Truck maintenance accidents 
by tools and equipment, U.S. surface 
mines, 1978-79, percent 

Handtools 30.3 

Elevated work platforms 15.3 

Servicing equipment 15.3 

Welding equipment 9.0 

Push-pull equipment 9.0 

Floor lifting equipment 7.5 

Slings and chains 5.0 

Support equipment 5.0 

Power tools 1.2 

Overhead lifting equipment 1.2 

Cleaning equipment 1.2 

Total 100.0 



CONCLUSIONS AND RECOMMENDATIONS 



The major factors in haulage truck 
maintenance accidents appear to be as 
follows: 

1. Lack of safety awareness or inabil- 
ity to measure and judge the job require- 
ment by either the employee or the 
supervisor. 

2. Poor access to working spaces, 
which forces the employee to take an 
unsafe position. 

3. Poor housekeeping. 

4. Poor equipment condition. 



The major goal of this paper has been 
to present truck maintenance recommenda- 
tions that are both technically and eco- 
nomically feasible, and are likely to 
have a high impact on safety while 
being acceptable to the industry. The 
approach has been to determine where and 
how maintenance personnel have been in- 
jured and to suggest how to alleviate 
specific hazardous situations. Many of 
the recommendations included in this 
report are already practiced by those 
mines where top management's commitment 
to safety leads to excellent safety 
records. 



5. Choice of the wrong tool or lack of 
proper tools. 



63 



PERFORMANCE-BASED TRAINING FOR MOBILE EQUIPMENT OPERATORS 
By Brett Collins , 1 Kris Krupp,2 and Richard L. Unger^ 



ABSTRACT 



To help upgrade and standardize the 
quality of training in the mining in- 
dustry, Woodward Associates, Inc., under 
contract to the Bureau of Mines, is 
developing and validating a performance- 
based training system for mobile equip- 
ment operators. The goals of the 



training system are to reduce injuries 
and fatalities, reduce equipment mainten- 
ance replacement, and increase productiv- 
ity of the overall mine operation. This 
paper presents the haulage truck training 
system as a case example. 



INTRODUCTION 



The benefits of skill and task training 
are now being realized by the mining and 
construction industries. More and more, 
training is turned to for increasing pro- 
duction and job satisfaction, and for 
reducing accidents, machine wear and 
abuse, and maintenance costs. 

Historically, training in the mining 
and construction industries has meant 
using one of two approaches. One was to 
hire "qualified" equipment operators and 
assume that these individuals knew enough 
about mining practices and equipment 
operation that they needed no instruction 
beyond simple commands. In the other 
case, where such "qualified" operators 
were not available, training meant leav- 
ing the new hire with an employee of long 
and proven experience until that employee 
decided that the new hire was "trained. " 
In neither of these cases were perform- 
ance standards employed — not in the 
selection of experienced operators since 
the definition of "qualified" varies from 
supervisor to supervisor, and not in the 
criteria by which the "experienced 
trainer" is able to judge the new employ- 
ee's developing skill. 

^Manager of engineering programs. Wood- 
ward Associates, Inc., San Diego, CA. 

^Training specialist. Woodward Associ- 
ates, Inc., San Diego, CA. 

^Civil engineer, Pittsburgh Research 
Center, Bureau of Mines, Pittsburgh, PA. 



To help upgrade and standardize the 
quality of training in the mining 
industry, a performance-based training 
system for mobile equipment operators is 
being developed and validated. This 
effort involves the application of proven 
adult educational methods to an industry 
that relies on very expensive, often 
large and diverse equipment which is 
operated in a hazardous and constantly 
changing work environment. The goals of 
training are to reduce injuries and 
fatalities, to reduce equipment mainten- 
ance and replacement costs, and to 
increase productivity of the overall mine 
operation. 

Work on the development of this train- 
ing system began in 1970. The system, as 
tailored for off-highway haulage truck 
operator training, is currently in use in 
an open pit copper mine in Arizona and 
two strip coal mines in Kentucky. 
Another version is in use at a highway 
truck driving school in California. A 
front-end loader version of the system is 
being validated in the field, and work is 
continuing on equivalent system applica- 
tions for eight other generic mobile sur- 
face mining machines (e.g. , dozers and 
scrapers). For the purpose of this 
paper, the haulage truck training system 
will be the example by which the system 
is presented. 



64 



HAULAGE TRUCK TRAINING SYSTEM 



The haulage truck training system is a 
structured method providing the knowledge 
and skills needed by operators of off- 
highway haulage machines. The three main 
characteristics of the training system 
are that (1) it is performance based, (2) 
it is instructor based, and (3) it pro- 
vides experience in recognizing and hand- 
ling normal, abnormal, and emergency 
operating conditions. Classroom teaching 
and on-machine demonstration and practice 
sessions are grouped into training ele- 
ments whereby the trainee acquires basic 
operating skills before building up to 
the more complex, higher level skills. 
An outline of the haulage truck training 
system elements follows: 



field demonstrations, practice sessions, 
and written and performance progress 
tests. 

The training system relies on the in- 
structor to ensure that it meets the 
needs of the trainees and of the facil- 
ity. Although the instructional frame- 
work is provided, the instructor will 
provide significant input as follows: 

1. Tailoring the program materials for 
the specific mine and equipment with 
which the trainee will be working. 

2. Determining the appropriate timing 
of presentations and practice sessions. 



Education Orientation, 



Introduction 



to mining and general mining techniques 
of the specific mine, and to the role of 
the haulage truck in that mine. 

Personal Protection , - Role and proper 
use of personal protective clothing and 
equipment, and of rollover protective 
structures and falling object protective 
structures, 

Preshift Procedures , - Introduction to 
machine systems, features, and controls; 
walk-around inspection procedures; pre- 
ventive maintenance and fluid level 
checks; startup and shutdown. 

Basic Operation . - Basic operation pro- 
cedures and techniques, hazards connected 
with operation, abnormal operating condi- 
tions (e.g., low air pressure). 

Advanced Operation , - Machine operation 
in the production cycle, special applica- 
tions of the machine (e,g,, dumping 
at the crusher) , night operation, emer- 
gency operating conditions (e,g,, brake 
failure). 

Proficiency Demonstration , - Final re- 
view, practice, and evaluation of knowl- 
edge and skills covered in training 
program. 

These elements are presented primar- 
ily in slide-tape formats which are 
supplemented by discussions, workbooks. 



3, Utilizing supplementary training 
aids and teaching-learning activities for 
remediation, as needed, 

4. Making the important decision as to 
whether the trainee should be advanced to 
the next element and, thereby, the next 
skill level. 

The training system is complete with 
guides, suggestions, and cues to help the 
instructor make some of these decisions 
(such as how to use the information from 
written and performance progress tests to 
determine if the trainee should advance) , 
But the instructor is all important when 
it comes to making the training work; he 
or she is the one who knows the kind of 
performance to look for. In the hands of 
an effective instructor, the training 
system takes the trainee to the desired 
skill level efficiently and effectively. 

The training system is performance 
based in that the trainee is continually 
evaluated as to developing skills and is 
not permitted to progress to the next 
element until he or she has demonstrated 
mastery of skills and knowledge at the 
present level. The in-field performance 
progress tests and the final proficiency 
demonstration are based on criteria that 
reflect the mine owner's requirements for 
performance, and no trainee is signed off 
as being "trained" until these criteria 
have been met. 



65 



To assist the instructor in both the 
teaching and the evaluation of new 
skills, a specially designed training aid 
called the on-board simulator of abnormal 
conditions (OBSAC) was developed for use 
with the training system. The OBSAC pro- 
vides an opportunity for the trainee to 
experience and respond to the abnormal 
and emergency conditions that are often 
the cause of accidents associated with 
the operation of mining machines. The 
OBSAC is a suitcase-size unit connected 
to a modified, but full functioning, 
haulage truck via an umbilical cord. 
When the OBSAC is not plugged into the 
haulage truck, the machine performs and 
functions normally in production. Be- 
cause the haulage truck can function as 
both a trainer and a productive unit, the 
concept of simulation becomes both cost 
effective and practical and, hence, 
highly desirable. 

With the OBSAC, the instructor can 
alter gauge readings on the haulage 
truck's console to give the appearance of 
changing machine conditions and malfunc- 
tions. Actual machine functioning is not 
altered during such simulations of ma- 
chine problems. While the specific 
machine gauges, indicators, and alarms 
that can be altered by the OBSAC vary 
from truck model to truck model, follow- 
ing are some of the more common compon- 
ents that are manipulated, and an example 
of what each can be made to represent: 



Gauge, indicator, 
or alarm 



Malfunction 



Oil pressure Oil leak. 

Water temperature. . Radiator leak. 

Voltmeter Discharging battery. 

Air pressure Loss of air pressure 

(brakes) . 

The instructor can also use the OBSAC 
to actually reduce or degrade certain 
machine functions to provide the trainee 
with the invaluable experience of 
responding to a machine failure. For 
example, a haul truck operator-trainee 
can have an actual experience of trying 
to stop the truck when up to 50 pet 
of the service braking capability is 
lost. This simulated degradation is 



accomplished via the BRAKE DEGRADE SWITCH 
on the OBSAC and occurs only as long as 
it is held in the ON position by the in- 
structor. Full hydraulic pressure is 
immediately restored when the switch is 
released. A total loss of braking capa- 
bility is not possible via the OBSAC, 
thereby allowing the instructor to retain 
control of the training environment and 
ensure safe use. Similarly, other truck 
features can be degraded (depending upon 
the truck model involved) , including the 
hydraulic steering system and the truck's 
propulsion system. 

A digital stopwatch is included on the 
OBSAC console to allow the instructor to 
document the lapsed time between the im- 
plementation of a malfunction or failure 
and trainee's recognition and response to 
the same. This particular feature is 
especially useful in teaching the im- 
portance of console scanning patterns for 
detection of potentially critical situa- 
tions before they do in fact become 
critical. One example would be a simu- 
lated loss of hydraulic steering pres- 
sure, which automatically initiates an 
auxiliary hydraulic pump on some machines 
to provide about 15 s of emergency steer- 
ing capability. If the loss of steering 
pressure and subsequent turning on of the 
auxiliary system is not immediately 
recognized, the limited emergency steer- 
ing capability may be expended before the 
operator can bring the machine to a safe 
stop. The built-in timer can aid both 
the instructor and the trainee in knowing 
if the trainee's response is appropriate 
and/or adequate for the situation. 

The OBSAC is integrated into all por- 
tions of the training system where actual 
machine procedures and operation are 
involved. For example, in the preshift 
procedures element, it can be used by the 
instructor to create an inappropriate 
prestart condition, such as insufficient 
control air, which must be detected and 
corrected before engaging the engine. In 
basic operating skills, it might be used 
to simulate a battery discharge during 
operation in the production cycle. When 
the operator-trainee is proficient in 
normal machine operation, the instructor 
could (in the advanced operation element) 



66 



degrade the brakes and observe how the 
trainee handles the situation. The 
trainee always has the benefit of immedi- 
ate feedback as to whether or not the 
response was correct. The instructor 
also has a timely opportunity to provide 
additional instruction as to how the 
problem should have been handled. 

Of course, the instructor must use the 
OBSAC with great care and discretion so 
as to avoid placing the machine, the 
trainee, him or herself, and others work- 
ing in the training or production area in 
jeopardy. Practice is required in order 
to preserve credibility and effective- 
ness; in other words, malfunctions must 
appear to occur as they would under real 
malfunction conditions. For example, few 
systems malfunction suddenly. They will, 
instead, deteriorate gradually over a 
period of seconds, minutes, or even 
hours, A considerable knowledge of 
machine functioning is prerequisite to 



the skillful use of the OBSAC as a train- 
ing aid. 

In addition to the training of new 
haulage truck operators , the haulage 
truck training system and the OBSAC are 
being used in annual refresher training 
of experienced haulage truck operators. 
Regular opportunities to practice skills 
that are seldom, if ever, needed insures 
that all haulage truck operators have 
acquired the appropriate skills to handle 
a given situation. Experimentally, this 
application is being taken one step fur- 
ther in the form of a haulage truck oper- 
ator's rodeo, where operators compete 
with each other for prizes. The goal is 
to encourage professional attitudes and 
the continual upgrading of skills on the 
part of the operators themselves to fur- 
ther decrease machine abuse and acci- 
dents, while increasing overall mine pro- 
duction and promoting job satisfaction. 



APPLICATIONS 



This training system has also been suc- 
cessfully applied to other surface mobile 
mining machines. The front-end loader 
training system will soon be field- 
validated at which time it will be made 
available for general use. The front-end 
loader training system can employ the 
OBSAC in much the same way the haulage 
truck training system does, but with the 
restriction that it is only appropriate 
for front-end loaders with cabs of suffi- 
cient size and design to permit the in- 
stallation of an appropriate buddy seat 
and seatbelt for the instructor. The use 
of remotely controlled versions of the 
OBSAC for machines that cannot be modi- 
fied to safely accomodate the instructor 
has been investigated and is viable, 
although expensive. 



The training system is also being 
applied to eight other generic types of 
surface mining equipment: track-type 
dozers (and front-end loaders), scrapers, 
rotary drills, carriage-mounted cranes, 
utility service trucks, shovels, fork- 
lifts, and motor graders. Preliminary 
studies and task analyses show the train- 
ing system to be totally viable for all 
of these generic machine types. The 
OBSAC, with modifications, is appropriate 
for the majority of these machines. How- 
ever, as with the front-end loader, ex- 
tensive machine alterations might be more 
expensive and/or structurally difficult 
to accomplish than would currently be 
cost effective to implement. 



SUMMARY 



The haulage truck and front-end loader 
training systems are now available for 
general use. The availability and dis- 
tribution of the OBSAC training aid is 
yet to be determined because of the 
model-specific considerations that must 
be incorporated into the construction of 



each OBSAC unit and because of the in- 
structor training necessary to ensure its 
safe and appropriate use. For more in- 
formation, contact the Bureau of Mines, 
Pittsburgh Research Center, P.O, Box 
18070, Pittsburgh, PA 15236, 



67 



STABILITY INDICATORS FOR FRONT-END LOADERS 
By Gilbert Wray^ and August J. Kwitowski^ 



ABSTRACT 



This paper describes the development of 
a stability-indicating system for use in 
minimizing the occurrence of front-end 
loader (FEL) rollovers in mining. The 
development proceeded in three phases: 
definition of FEL stability-instability 
characteristics; design of a first- 
generation stability indicator; and de- 
sign of a simplified, second-generation 



stability indicator. Goals met by the 
final design include confirmation of a 
simplified methodology for detecting 
machine instability; the ability to be 
installed on new loaders during manufac- 
ture or on older loaders on a retrofit 
basis; and reliable, easily interpretable 
operation. 



INTRODUCTION 



Rubber-tired FEL's, originally intended 
as small machines for handling loose or 
stockpiled material, have rapidly in- 
creased in both size and number at sur- 
face mine operations over the past 15 to 
20 yr. Statistics bear out the fact that 
FEL accidents form the largest single 
category of machinery-related accidents 
in surface mining. For the years 1975 
through 1981, FEL's used by the mining 
industry were involved in 26 fatalities 
and numerous less severe accidents.^ The 
vast majority of the fatalities occurred 
as a consequence of the FEL's rolling 
over and either crushing the operator 
within the cab or the operator being 
struck by the machine after jumping or 
being ejected from the cab. 

Rollover protective structures are re- 
quired on FEL's as specified in the Code 
of Federal Regulations, Title 30, Fart 
7 7.403a, "Mobile Equipment, Rollover Pro- 
tective Structures (ROPS)." Obviously, 
ROPS do not prevent the vehicle from rol- 
ling over, but offer protection to the 

^ Chief, vehicle mechanics and develop- 
ment division, Stevens Institute of 
Technology, Hoboken, NJ. 

^Civil engineer, Pittsburgh Research 
Center, Bureau of Mines, Pittsburgh, PA. 

^Computerized sort of Mine Safety and 
Health Administration Health and Safety 
Analysis Center data conducted February 
1983. 



operator in the event that the vehicle 
does roll over. At present, FEL opera- 
tors have only their own judgment against 
which to evaluate the stability or insta- 
bility of their machines. 

The Bureau of Mines , through contract 
J0395074 with the Stevens Institute of 
Technology, has responded to this prob- 
lem with the development of a FEL stabil- 
ity indicator that provides the operator 
a reliable, easily interpreted display of 
the stability status of his or her ma- 
chine. The stability indicator was de- 
signed to be a relatively low cost 
item capable of being retrofitted to 
older FEL's or incorporated into new 
loaders during their manufacture. Strain 
gage instrumentation is used to monitor 
the magnitude and rate of change of 
forces acting normal to the loader's 
wheels , with these forces being direct 
indicators of the machine's center of 
gravity relative to its stance on the 
terrain. The relative stability of the 
loader is conveyed to the operator 
through a display of green, amber, and 
red lights. 

The development of the present stabil- 
ity indicator was undertaken in several 
stages; first, the stability characteris- 
tics of FEL's were analyzed and mathe- 
matically modeled; second, a first- 
generation stability indicator was built 
that compared the calculated analog 



68 



values to the measured values and Issued 
a warning to the driver based on that 
difference as a safety margin; and third, 
the present device was produced, where 
the whole machine is used as the analog, 
and the results of the interpretation of 
the actual wheel loads on the ground are 
used to warn the driver of an impending 
overturn situation. 

DEFINITION OF LOADER STABILITY 
CHARACTERISTICS 

More than half of rollover accidents 
occur when the loaders are being trammed; 
that is , when they are being transported 
under their own power from one work area 
to another, when they are being moved 
from the working areas to maintenance 
shops and fueling stations , or when they 
are traveling over distances greater than 
those covered in normal loading and 
unloading operations. Generally, the 
loader operates at greater speed while 
tramming than it does during its normal 
work cycle. Eight out of ten tramming 
accidents occur on downgrades. 

Front and side slopes contribute to an 
unstable operating mode of the FEL. 
Operator-controlled factors contributing 
to the loss of stability are the weight 
of the load in the bucket, the bucket 
height, the yaw angle of articulation, 
its velocity, and the degree of braking. 
While any one of these parameters could 
be a principal contributor, it is usually 
a combination of these factors that pro- 
duces an accident. 

The first step towards alleviating the 
rollover problem was to define and quan- 
tify the following critical combination 
of factors and conditions that are 
most pertinent to front-end loader 
instability: 

Vehicle pitch angle 

Vehicle roll angle 

Bucket load 

Bucket location 



Vehicle articulation angle 

Inertial loads (acceleration- 
deceleration, centripetal forces) 

A device that is to indicate to an opera- 
tor just how close the machine is to an 
overturning condition has to account 
for the combined influence of all these 
factors on the stability characteristics 
of the vehicle. 

MATHEMATICAL ANALYSIS OF STATIC LOAD 
AND INCLINATION LIMITS 

The basic calculations of the static 
overturn limits for FEL's have to include 
all the variations possible in vehicle 
geometry. These calculations can be di- 
vided into two parts: locating the cen- 
ter of gravity (CO) of the loaded machine 
and determining whether this CG location 
relative to the support points induces 
overturn. 

Most FEL's have a three-point suspen- 
sion system. The rear axle is pinned to 
the frame at or above the axle center, 
creating a transverse walking beam ac- 
tion. This pin joint represents a single 
suspension point. The other two points 
are the ground contact points of the 
front tires (fig. 1). With this type of 
suspension, the effective masses and CG's 
for pitch overturn are different from 
those for roll overturn. The vehicle 
will overturn about the front axle (nose 
down) if the CG of the entire mass is in 
front of a line connecting the front 
wheel ground contact points (fig. 2). 

Roll overturn can arise if the CG lies 
outside the line joining either of the 
front wheel ground contact points and the 
rear suspension pin (fig. 1). In this 
latter case, the mass involved is that of 
the loaded vehicle less the mass of the 
rear axle unit. This mass is called the 
main mass. 

There is, by design, a limit to the ro- 
tation possible about the rear axle (usu- 
ally about 15°) after which the rear 
wheel contact point becomes the third 



69 




FIGURE 1.- Front-end load- 
er suspension points under 
normal conditions. 




yfiv 



FIGURE 2, - Projection of center of gravity near 
overturn. 



support point (fig. 3). A machine that 
has tipped enough to reach this limit 
will have enough momentum to overturn 
completely. 

Three variables affect the CG loca- 
tion with respect to the vehicle. The 
first variable is the articulation angle. 
To obtain the variation of CG with 
articulation angle, the weight and CG 




FIGURE 3, - Front-end 
loader suspension points 
near overturn. 



locations of both the front and rear 
units are needed. To obtain the CG of 
the main mass, the mass of the rear axle 
and its tires (plus ballast) has to be 
subtracted. The other two variables en- 
tering into the CG computation are the 
bucket load and the position of the lift 
arm. From this information, the loca- 
tions of each of the masses and the loca- 
tion of the CG's can be obtained in the 
standard manner of summing moments and 
dividing by the total weights. In addi- 
tion, the position of the vehicle is 
identified by the pitch and roll angles 
(i.e., the angles between the gravity 
vector and the vehicle's x-y and x-z 
planes, respectively). 

The CG is located with respect to a 
vehicle coordinate system whose origin is 
at the center of the front axle, with the 
X-axis pointing forward, the y-axis to 
the right, and the z-axis down (fig. 4). 
The mathematical procedure used is to 
locate the vehicle on a horizontal ground 
plane with a selected bucket load, lift 
arm position, and articulation angle. 
The ground plane is then inclined to a 
combined front and side slope, and the 
vertical projection of the vehicle CG is 
determined. If this projection falls 



70 




FIGURE 4, - Coordinate system used 



in analysis. 



within the stability triangle, the ma- 
chine is considered statically stable; if 
it falls outside the triangle, it is 
statically unstable. 

A computer program was written to solve 
these equations iteratively, as the m^ost 
economical procedure is to establish ap- 
proximate limits of the machine and to 
refine the results by calculating small 
increments of change. The final pitch- 
rollover points are easily determined to 
within 0.2°. The final solutions to the 
stability equations are then plotted by 
the computer. 





- 


1 ' 1 ' 




1 ' 


1 1 


80 


- 




^ 




_ 




- 


—~-^I-, 


^ 


10,000 lb 

^ i 


60 


- 


/y 




\v- ° "^:^ 


_ 




• 




- 


|40 


- 








- 


uj" 

2 20 

< 


"f 








^ 


io 


- Q. 

3 








- 


c 

■1 








- 


-20 


-1 


\ Bucket loads, lb 




- 






\^ IO.OOOn ' 


-/ 




-40 


- 


=^ 


- 






, N-i^- 


1 


- 


-60 




-40 -20 C 


) 


20 40 60 



ROLL ANGLE, deg 



FIGURE 5. - Stability envelope for ormat carry 
and articulation = 0°. 

reduced in size with the lift arm in the 
full-up position. Figures 7 and 8 show 
the stability envelope when the vehicle 
is articulated to 35° and are directly 
comparable with figures 5 and 6 (without 
articulation) . 



STATIC OPERATING ENVELOPES 

Using the above procedure, the static 
stability limits as functions of pitch 
and roll angles were generated with the 
bucket load, articulation angle, and lift 
arm position as independent parameters. 
Figure 5 is a plot of the pitch angle 
versus the roll angle with the bucket 
load as a parameter for 0° articula- 
tion angle and with the lift arm at the 
"carry" position. The FEL is stable for 
any combination of roll and pitch angle 
within the stability "triangle." Figure 
6 is a similar plot except that the lift 
arm is in the "full-up" position. As is 
expected, the operating envelope is 



The articulation angle produces mirror 
image curves; the -35° articulation curve 
is inclined equally and in the opposite 
direction to the +35° articulation angle 
curve . 

The curves readily show that it is nec- 
essary to sense and respond to all the 
parameters. To sense merely roll angle 
would have two opposite and unacceptable 
effects : 

1. It could result in a warning device 
that is far too conservative and hence 
restricts the operation of the FEL to 
an unacceptable level and prevents its 
acceptance. 



71 



80 



60 



40 



CD 



20- 



-20 



•40- 



10,000 Ib^ 




-60 
-40 -20 20 

ROLL ANGLE, deg 

FIGURE 6. - Stability envelope for arm full-up 
and articulation = 0°. 



2. It may not give a warning when it 
should, producing false confidence which 
might contribute to an accident. 

These results have been compared with 
available experimental data from one of 
the manufacturers and have been found to 
correlate well (tables 1-2). 

STATIC STABILITY CORRELATION EQUATION 

To be able to construct the electronic 
logic circuitry for the first-generation 
stability indicator, the stability enve- 
lope had to be mathematically defined. 
However, describing all the curves with 
one equation was quite difficult because 
the curves are triangular in shape and 
lie in all four quadrants. All attempts 



-60 




60 



-20 20 
ROLL ANGLE, deg 

FIGURE 7. - Stability envelope for arm at carry 
and articulation = +35°. 



at generating a correlation equation by 
utilizing a systematic, logical, theoret- 
ical approach failed. Therefore, an al- 
ternate solution was used. 

An initial decision was made that roll 
angles greater than 30° (about a 60-pct 
side slope) and pitch angles beyond the 



TABLE 1. 



Center of gravity comparison 





Distance from 

reference 

axis , in 




Manufac- 
turer's 
data 


Calcu- 
lated 
values 


Bucket empty, arm at 
carry: 

Longitudinal (x) 

Lateral (y) 

Vertical (z) 

Bucket loaded (10,500 
lb) , arm full-up: 

Longitudinal (x) 

Lateral (y) 

Vertical (z) 


60.9 



-11.2 

82.9 



-59.7 


60.9 



-11.2 

82.9 



-59.7 



72 



TABLE 2. 



Inclination limit comparison 





Side 


slope angle 




at 


overturn. 


FEL position 




deg 






Manufac- 


Calcu- 




turer 


's 


lated 




data 




values 


Bucket empty, arm at 








carry: 








Facing up slope 


56 




56.4 


Facing down slope.... 


56 




58 


Parallel to slope.... 


38 




39 


Bucket loaded (10,500 








lb) , arm full-up: 








Facing up slope 


42 




42.9 


Facing down slope.... 


22 




26 


Parallel to slope. . . . 


19 




19 



range of +35" (up) to -25° (down) would 
be considered outside the normal range 
of operation. Separate limit detectors 
would be employed to trigger a warn- 
ing light if any of these basic limits 
were exceeded, regardless of any other 
condition. The equation of a parabola 
that includes the effects of bucket load 
and lift arm position but not of articu- 
lation angle has the form 

Or = C, + C2W + C3 e^p^ - (C4ep + €5)2, 

where Sr = roll angle, 

9p = pitch angle, 

^arm - lift arm angle, 

W = bucket load. 



and 



To correct for articulation angle (69^+) 
replace 



and 



Gp by epCos.4eart - erSin.4ear+ 
V by epSin.4ear^ + e^Cos.4ea,t. 



and the prediction equation for the cri- 
tical roll angle, including articulation 
angle and specific constants for a spe- 
cific FEL becomes 



60 



-a 

LU 

_l 

< 

X 

o 



40 



20 



-20- 



■40 



-40 



' 1 1 

Olb^ 
10,000 Ib'i^" 


. 


\ 


"^^ 


g/// Bucket lead, lb Ij 

i/f^-^o,ooo^_y/ 


1 


- 


V 5,000^ / 


1 


. 1.1,1 




1 



-20 20 

ROLL ANGLE, deg 



40 



C 1 , C2 > C-! 



constants. 



FIGURE 8. - Stability envelope for arm full-up 
and articulation = +35°. 



73 



■"cri t ica I 



36.94 - 3.265 x IQ-'^W - 0.2239 egrm 

- [0.054 (epCos.4eapt - rSin.4ear+) 
+ 2.1577]2. 



The absolute value of Or ,^, , was 
1^ . -, . cr i t i ca I 
used since the stability curves are 

mirror images and the equation is val- 
id for either positive or negative 



articulation angles. This absolute value 
ue of 



was then compared with 
LI angle so that tt 
safe operating range was represented by 



the corrected roll angle so that the 



,Sin.4eart + erCos.4eart 



Figure 9 is a correlation plot of the 
critical roll angle predicted from the 
equation versus the roll angle calculated 
by the computer program. The correlation 
is made for a fixed articulation angle of 
20° , but for three bucket loads . The 
individual data points represent three 



lift arm positions (carry, horizontal, 
and full-up) at various combinations 
of pitch angle. This prediction equa- 
tion thus contains all of the terms that 
enter into the determination of static 
stability. 




20 



10 
TRUE, e^ 

FIGURE 9. - Correlation of data between predicted and actual cases. 



30 



40 



74 



FIRST-GENERATION STABILITY INDICATOR 



ANALOG CIRCUIT 

An analog circuit was designed to solve 
the prediction equation, A block diagram 
of this circuit is shown in figure 10. 
The seven electronic circuit cards used 
are shown in figure 11, This analog com- 
puter was used to solve the correlation 
equation from sensor Inputs, and then 
compare the existing roll angle to the 
critical roll angle, and give the driver 
a visual warning. 

SENSORS AND TRANSDUCERS 

The original approach to sense the 
pitch and roll angles by damped pendulum- 
type potentiometers was abandoned because 
their range of natural frequency coin- 
cides with that of FEL's, at approximate- 
ly 2 Hz. Therefore, electrolytic sen- 
sors, using a semiconducting fluid in a 
circular tube and with a natural fre- 
quency greater than 10 Hz, were selected. 



The articulation angle and lift arm po- 
sition were sensed by single-turn rotary 
potentiometers. Special shaft bearing 
and seal designs made these potentiome- 
ters safe from salt spray, sand, dust, 
and fungus. 

The bucket load was determined by sens- 
ing lift cylinder hydraulic pressure with 
a pressure transducer and combining it 
electronically with lift arm position. 

The speed sensor was a dc tachometer- 
generator friction- coupled to the output 
shaft of the transmission. 

WARNING INDICATORS 

The driver's warning device consisted 
of four indicator lights. One was green, 
two were amber, and one was red. The an- 
alog circuitry accepted the five sensor 
Inputs, calculated the angle at which the 
machine would roll over, and compared 



'art 



Absolute 
value 



Direction 
trigger 



Extreme 

limit 
detectors 



Extreme 

limit 
detectors 



C 



Summary 



Sine 



Signal 



Cosine 



Load 
calculator 



P 



' Hydraulic pressure 

I Speed (V) 

I 4 



Square 



Multiplier 



I 



Multiplier 



Multiplier 



Multiplier 




Summary 

and 
absolute 

value 



Summary 



Square 



I 



^ Summary 



Limit 
detectors 



Limit 
detectors 



Limit 
detectors 



Limit 
detectors 



I \ ] I 



FIGURE 10. - Block diagram of signal processor. 



75 





FIGURE 11. - Electronic circuit boards for first-generation stability indicator. 



this value to the corrected roll angle. 
The difference between the calculated an- 
gle and the actual roll angle was repre- 
sented by a voltage that was sensed by 
four level detectors. Each level detec- 
tor was wired to one of the lights and 
was adjustable for proper level and 
sequencing. 

EVALUATION 

The above-described system was in- 
stalled on three FEL's used in a 
rock quarry operation. During a 12-iuonth 
test period, the units performed sat- 
isfactorily and were judged by the 



operators as very useful operational 
tools. However, these first-generation 
units had several disadvantages, as 
follows: 

1. They were costly to manufacture ow- 
ing to the complexity of the electronics. 

2. They were costly to install owing 
to the skilled labor required to install 
the sensors. 

3. The system would not completely 
correct for the effects of inertia during 
braking, acceleration, or cornering. 



THE SECOND-GENERATION STABILITY INDICATOR 



In an effort to reduce the complexity 
and cost of the system, an alternate 
means of obtaining a signal or measuring 
a parameter that would indicate rollover 
instability was sought. As the FEL ap- 
proaches rollover instability, the CG 
moves towards the outside of the "stabil- 
ity triangle" formed by the three support 
points. As this happens, the normal load 
on the up-slope wheel decreases and the 
normal load on the down-slope wheel 
increases. At the point of rollover 



instability, the normal load on the up- 
slope wheel has been reduced to zero. 

The task of designing a stability indi- 
cator has now been reduced to designing a 
method of sensing the normal load on each 
of the front wheels and using the lower 
value to trigger a warning system. 

By utilizing strain gages, the bending 
stresses in the axle can be determined. 
To obtain the normal load from the 



76 



measured axle bending stresses, it is 
necessary to measure, or devise a system 
to cancel out, the bending stresses in 
the axle due to the tire side forces. 
These tire side forces are generated to 
resist the dovmslope forces acting on the 
FEL; they can also be generated during 
steering. The tire side force acting at 
the ground plane creates a bending moment 
in the axle which is proportional to the 
wheel radius. By measuring the axle 
bending stresses at two planes, they can 
be subtracted, which cancels out the ef- 
fects due to tire side force, leaving a 
measurement that is proportional to wheel 
normal load. 

Referring to figure 12, bending moment 
at plane 1 is 

M2 = NL(L2) + SF(r). 

Bending moment at plane 2 is 

M2 = NL(L2) + SF(r) 

M2 - Ml = NL(L2) - NL(Li) 

= NL(L2-L,) 

or NL = M2 - Mi/(L2 - L,). 



The bending moments at planes 1 and 2 
are measured using strain gages and, 
since the distance between the two planes 
is known, the normal load is determined. 

AXLE SENSORS 

To measure the bending strains on the 
FEL axle, it was decided that some form 
of bonded strain gage or strain trans- 
ducer would have to be used. Since the 
output of a strain gage is represented by 
a voltage and the voltages obtained from 
the two planes must be subtracted, it was 
decided that a full-bridge configuration 
must be used in order to retain a usable 
signal level. A full-bridge configura- 
tion will produce four times the signal 
output of a quarter bridge and is inher- 
ently temperature compensated. 

In an effort to find a simple, easily 
installed, field method of sensing the 
axle strains so as to reduce the overall 
system cost, several methods were tested 
and rejected or refined, as follows: 

1. Strain gages bonded directly to the 
axle. These were field-tested and re- 
jected owing to excess j-ve installation 




NL 
SF 



KEY 

Normal load on wheel 
Side force on wheel 

Distances from tire centerline 
to measurement plane 

FIGURE 12. - Forces acting on wheel of front-end loader. 



77 



cost and cost of replacement or repair. 
Highly skilled labor was required. 

2. Weldable strain gages directly 
spot-welded to the axle. These were 
field-tested and rejected owing to zero 
shifts caused by the lack of an extremely 
flat surface to mount on. 

3. Strain link manufactured and 
strain-gaged in shop; installed by direct 
welding to the axle. These were field- 
tested and rejected owing to the diffi- 
culty of preventing gage damage due to 
heat conduction during welding. 



At the present time, two fastening 
methods are being tested. The strain 
links on one side of the FEL axle are 
bolted to the mounting blocks using 3/8- 
in socket-head cap screws. The strain 
links on the other side of the axle are 
bonded to the mounting blocks. The bond- 
ing method is quite simple, using pre- 
packaged epoxy, and requires little 
skill. In addition, the strain link does 
not experience any zero shift, due to 
bolting torque, when it is bonded, thus 
reducing the electronic adjustments 
required. 



4. Strain links manufactured and 
strain-gaged in shop. These are attached 
to mounting blocks which are welded to 
the axle using a welding fixture. This 
method was refined as described in the 
following paragraphs. 

Two methods of attaching the strain 
links to the mounting blocks , bolting and 
bonding, are presently under test on a 
Government-owned JD-544 FEL at the Bureau 
of Mines facility in Bruceton, PA. 

The strain link was designed so as to 
incorporate a mechanical gain of 3:1. 
This was accomplished by machining the 
surfaces and narrowing the cross section 
so that the elongation that should occur 
over a 1.5-in length is concentrated in a 
0.5-in section where the strain gages are 
located. All strain gaging and intergage 
wiring is performed on the strain links 
at the time of manufacture so that the 
field installation consists only of at- 
taching the strain link to the axle and 
connecting the output cable (fig. 13). 

The attachment method was designed so 
as to require a minimum of expertise and 
time. Three mounting blocks for each 
transducer are held against the axle by a 
simple welding fixture, and the blocks 
are welded to the axle. The strain link 
is then either bonded or bolted to the 
mounting blocks , and the mechanical in- 
stallation is complete (fig. 14). 




FIGURE 13. - View of strain links. 



78 




FIGURE 14. - Strain links installed on front- 
end loader axle. 



FIGURE 15. - Electronic circuit board for 
second-generation indicator. 



ELECTRONIC SIGNAL CONDITIONING 
AND DISPLAY 

The electronic signal conditioning 
package has been considerably simplified. 
It is no longer necessary to perform 
various computations to evaluate a 
lengthy correlation equation as was the 
case with the original system. The new 
system consists of four integrated cir- 
cuit instrumentation amplifiers to in- 
crease the signal levels from the strain 
links, a buffer amplifier to sum (sub- 
tract) the signals from different planes, 
a differentiating circuit, a quad- 
comparator, power darlingtons to drive 
the warning lights, and a power supply. 
The entire electronics system, including 
power supply, is now contained on a 
single 4-1/2- by 6-1/2-in printed circuit 
card (fig. 15). For simplicity and to 
expedite the initial field test, the 
single card is shown mounted in the same 



National Electrical Manufacturers Associ- 
ation enclosure previously used (fig. 
16) , allowing the use of the existing 
wiring and connectors. 

In an effort to take into account the 
effects of inertia and anticipate them, a 
differentiator circuit has been incorpo- 
rated. This circuit accepts the normal 
wheel load as an input and outputs a sig- 
nal proportional to the rate of change 
with respect to time of the normal wheel 
load, i.e., the first derivative. When 
the wheel load is positive but decreasing 
at some rate, the derivative will be a 
negative value whose magnitude depends on 
the rate of decrease. This negative- 
valued derivative is summed with the ori- 
ginal signal to produce a new normal load 
signal, which is lower in value than the 
original, by some amount depending on the 
rate of decrease, and therefore turns on 



79 



the warning lights earlier. By using a 
diode to limit the derivative to only 
negative values , the warning lights re- 
spond "normally" for increasing wheel 
loads. Figure 17 shows a representative 
signal for wheel load which is varying as 
a 1.5-Hz sine wave. Superimposed on top 



of the original signal is the "new" wheel 
load signal summed with its derivative. 
As can be seen, the voltage level is 
lower for the new signal when it is 
decreasing in value and is identical for 
increasing values. 



CONCLUSIONS 



Although field testing of the second- 
generation stability indicator has not 
yet been completed, all indications to 
date are positive. The design of the 
stability indicator — 



Additional information on the above- 
described stability indicator may be ob- 
tained from August J. Kwitowski , Bureau 
of Mines, P.O. Box 18070, Pittsburgh, PA 
15236, (412) 675-6474. 



1. Allows for its easy incorpora- 
tion on new front-end loaders during 
manufacture. 



2. Permits its installation on older 
loaders on a retrofit basis. 

3. Has resulted in reductions of size, 
complexity, and associated cost to the 
limit of practicality. 

Extensive testing of a prototype ver- 
sion of the stability indicator on a 
Government-owned FEL has shown — 

1. The methodology of sensing machine 
stability as a function of normal wheel 
loads is practical and works. 

2. The strain link method of sensing 
the normal wheel load provides an ade- 
quate signal of wheel load and removes 
the influence of side forces on the 
wheel. 

3. The strain link method allows for a 
quick field installation using a minimum 
of highly skilled personnel. 

4. The exact method of attaching the 
strain link, bonded or bolted, is yet to 
be decided based on the results of tests 
in progress. 



^'^i-j--^'.^^ 




FIGURE 16. - Second-generation stability in- 
dicator mounted in original enclosure. 



80 



k:^^:;^.^^-::^; 




FIGURE 17. - Oscilloscope trace of normal load signal and normal load signal summed with its 
derivative. 



81 



BULLDOZER NOISE CONTROL 
By R. C. Bartholomae'' and T. G. Bobick2 



ABSTRACT 



Bulldozer noise is the most serious 
noise problem for surface miners today. 
Not only are bulldozers the most common 
type of mobile equipment, but the major- 
ity of their operators are also exposed 
to more noise than current Federal regu- 
lations allow. In 1977, the Bureau of 
Mines responded to this problem by devel- 
oping retrofit noise control treatments 
that reduce the noise that reaches the 



operator. These treatments were specifi- 
cally designed to be readily installed in 
the field at low cost. In 1978, these 
treatments were installed on two Cater- 
pillar D9G's and an International Har- 
vester TD-25C in surface coal mines to 
demonstrate the noise reduction that can 
be achieved under actual production con- 
ditions. This paper presents the results 
of the field demonstrations. 



INTRODUCTION 



Table 1 shows the relationship between 
operator noise level and allowable expo- 
sure time mandated by the Federal noise 
regulations. Exposure to a continuous 
noise level of 90 dBA is permitted for no 
more than 8 h. For every 5-dBA increase 
in operator noise level, the allowable 
exposure time is cut in half. As an ex- 
ample, no more than 4 h of exposure is 
permitted when the noise level is 95 dBA. 
Also, there is an upper limit on noise 
intensity; exposure to continuous noise 
levels above 115 dBA is not permitted. 

Simply put, miners are overexposed to 
noise when their actual exposure time ex- 
ceeds the allowable time. 



TABLE 1, 



8 


Duration, 
h/d 


Noise level, 
dBA 

.... 90 


6 






. . . . 92 


4 






. . . . 95 


3 






. . . . 97 


2 






.... 100 


1-1/2. 






.... 102 


1 






. . . . 105 


3/4... 






.... 107 


1/2... 






.... 110 


1/4 or 


less 




115 



MINING NOISE CONTROL RESEARCH 



The Bureau of Mines has an ongoing re- 
search program in support of the noise 
regulations mandated by the Mine Safety 
and Health Act of 1977. This research 
program has two basic objectives. The 
first is to assess the impact due to 
noise and vibration on mine worker occu- 
pational health. The second objective, 

^Supervisory electrical engineer, 
Pittsburgh Research Center, Bureau of 
Mines, Pittsburgh, PA. 

^Mining engineer, Pittsburgh Research 
Center, Bureau of Mines, Pittsburgh, 
PA. 



which is more ambitious, is to develop 
feasible noise control technologies aimed 
at improving those instances when mine 
workers are overexposed to noise. 

Field surveys are used to assess the 
impact that noise and vibration have on 
mine worker occupational health. These 
surveys yield two kinds of technical in- 
formation. They identify the prevalent 
sources of noise and vibration peculiar 
to the mechanized mining environment, and 
they provide an estimate of the mine 
worker population overexposed to noise. 
Stated differently, the results of these 



82 



surveys identify acoustical problems in 
mining equipment and help to define and 
rank mining noise control research 
problems. 

In 1977, the Bureau of Mines conducted 
a noise survey of the surface coal mining 
industry.^ The results of this survey 
are presented in table 2. This table 
shows that bulldozers present the most 
serious noise problem in surface coal 
mining since they account for the most 
cases of equipment operator noise over- 
exposure. In fact, about 48 pet of all 
cases of noise overexposure at surface 
coal mines are due to bulldozers. 



coal mining are Caterpillar D9's. Taken 
together, Caterpillar D9's and D8's 
account for almost two-thirds of the 
bulldozers in operation at surface coal 
mines today. Because of the large number 
of Caterpillar D9's in operation, the 
Bureau of Mines sponsored a research pro- 
ject in 1978 aimed at developing and, la- 
ter, field-demonstrating feasible bull- 
dozer noise control technology for two 
Caterpillar D9G's: one equipped with a 
rollover protective structure (ROPS) and 
no cab, the other equipped with a stan- 
dard cab. In 1979, this noise control 
technology was also adapted to an Inter- 
national Harvester TD-25C. 



TABLE 2. - Total noise overexposure 
by machine type, U.S. surface coal 
mines, 1977 



TABLE 3. - Total bulldozer population 
by specific model, U.S. surface 
mines, 1977 



Equipment type 



Pet 



Bulldozers. 48.0 

Front-end loaders 15.5 

Haulage trucks 8.5 

Highway trucks .5 

Scrapers 5.5 

Draglines 8.0 

Overburden drills 2.0 

All others 12.0 

The surface coal mine survey also pro- 
vided information about the relative num- 
bers of each kind of equipment , broken 
down by manufacturer. Table 3 gives this 
information for bulldozers. Better than 
45 pet of the bulldozers used in surface 



Specific model Pet 

Caterpillar D9 47 

Caterpillar D8 17 

International Harvester TD-25 11 

All others 25 

It should be noted that the second most 
serious noise source in surface coal min- 
ing is the rubber-tired front-end loader. 
Because of some design similarities, the 
bulldozer noise control technology can be 
extended to rubber-tired front-end load- 
ers. The Bureau has also sponsored a re- 
search project that demonstrated the 
applicability of the retrofit noise con- 
trols on front-end loaders. 



NOISE CONTROL TREATMENTS FOR BULLDOZERS 



Since this project involved treatment 
of in-service machines, modification of 
the noise sources on the dozers was 
specifically excluded from considera- 
tion. Instead, retrofit noise control 

•^Ungar, E. E., D. W. Anderson, and 
M. N. Rubin. The Noise of Mobile Ma- 
chines Used in Surface Coal Mines: Oper- 
ator Exposure, Source Diagnosis, and 
Potential Noise Control Treatments (con- 
tract J0166057, Bolt Beranek and Newman 
Inc.). BuMines OFR 98-79, 1978, 117 pp. ; 
NTIS PB 299 538/AS. 



treatments were developed to limit the 
level of noise reaching the operator 
through various paths. Two design cri- 
teria were applied to the noise control 
treatments that were developed. Obvious- 
ly, they had to provide a measure of 
noise reduction for the operator; equally 
important was that, once installed, the 
modifications were not supposed to de- 
grade the overall performance of the 
bulldozer. In other words, the treat- 
ments could not adversely impact the nor- 
mal operation of the bulldozer or impose 
unusual maintenance requirements. 



83 



The instrumentation system used to re- 
cord the sound pressure levels in the 
operator compartment consisted of a 1/2- 
in-diam condenser microphone mounted on a 
preamplifier. The preamplifier was pow- 
ered by a portable battery box that was, 
in turn, connected to a stereo tape rec- 
order. The preamplifier was suspended 
from the ceiling of the operator cab so 
that the microphone (fitted with a wind- 
screen) was approximately 6 in from the 
operator's right ear. The recorded mag- 
netic tapes were analyzed using a one- 
third-octave-band real-time analyzer. 

Two general types of tests were made: 
static and moving. The static tests were 
made with the dozer running at high 
idle and with the torque converter under 
load. The latter test (which emphasizes 
exhaust tones) requires that the dozer 
be put in first gear and the brakes ap- 
plied to prevent it from moving. For 
either test, the engine was running at 
full throttle. 

The in-motion tests were performed 
according to SAE Recommended Practice 
J-1166. For these tests, the tape rec- 
order operator followed alongside the 
dozer using a long extension cable to 
connect the preamplifier and tape 
recorder. 



The data recording system was cali- 
brated before and after testing. Using a 
pistonphone, a 124-dB-at-250-Hz calibra- 
tion tone was recorded on the tape and 
used to calibrate the real-time analyzer 
during the tape playback. After calibra- 
tion, background sound level measurements 
were made to ensure that there were no 
other significant noise sources in the 
test area that would interfere with the 
measurements. 

In general , it was found that uninter- 
rupted airborne paths were the predomi- 
nant way for noise to travel to the 
operator. Structure-borne noise was im- 
portant only for the dash panel and cowl- 
ing, which were directly connected to 
the engine. The most effective treat- 
ments, therefore, were those that blocked 
the line of sight between the main noise 
sources (the engine and fan) and the 
operator, and the sealing of all openings 
near the floor pedals and the operator's 
seat to reduce the noise from the second- 
ary sources: the transmission and the 
final drive. Installation of sound ab- 
sorption material in the operator's area, 
primarily on the underside of the canopy, 
was also an effective noise control 
treatment. 



RESULTS 



The Caterpillar D9G dozer, which was 
equipped with a ROPS only, is shown in 
its final noise-controlled configuration 
in figure 1. The only treatments visible 
in the photograph are the muffler and the 
windshield that was installed to block 
the airborne noise between the engine and 
fan and the operator. The various treat- 
ments are itemized in table 4 along with 
the corresponding noise reduction that 
each treatment provided for the high-idle 
condition. Note that about 6 dBA of re- 
duction was obtained by three major 
treatments: installing the windshield, 
applying the muffler, and installing the 
sound absorption material under the 
FOPS (falling object protective struc- 
ture) canopy. The remaining 5.5 dBA of 



reduction was obtained by carefully seal- 
ing all openings and by isolating the 
dash and cowling from the vibrating en- 
gine. The cost of the entire treatment 
package was less than $1,000 for materi- 
als and required about 100 employee-hours 
for installation. 

The Caterpillar D9G dozer with the cab 
is shown in figure 2, The noise control 
treatments are located inside the cab and 
therefore are not visible in the figure. 
Table 5, however, lists the treatments 
that were utilized. 

Following installation of the noise 
control treatments, the dozers were 
placed in service during March and April 



84 



1978. Both are currently operating in noise was 93 to 94 dBA, during normal 
surface coal mines in the Eastern United operation. This indicates that the dozer 



States. 

Noise dosimeter readings taken on 
the operator of the ROPS-only dozer 
indicated that the time-weighted average 



will be in compliance with Federal regu- 
lations , without requiring hearing pro- 
tection for the operator, for 4-1/2 
to 5-1/4 h/d. Dosimeter readings taken 
on the dozer with the cab gave the 



TABLE 4. - Summary of noise control treatments installed 
on ROPS-only-equipped dozer (high idle) 



No, 



Treatment 



Sound level. 
dBA 



Noise reduction 

from baseline, 

dBA 



None (baseline) 

Lexan windshield 

Absorption under FOPS 

Exhaust muffler 

Windshield and absorption 

Treatment 5, plus muffler , 

Treatment 6, plus dash seals and 
isolation 

Treatment 7, plus floor seals..., 

Treatment 8, plus seat seals 

Treatment 9, plus tank seals and 
hydraulic valve cover 



105.5 
101.5 
102.5 
104 
100 
99.5 

96.5 
95.5 
95 

94 





4 

3 

1.5 

5.5 

6 

9 

10 
10.5 

11.5 




FIGURE 1. - Noise-controlled ROPS-only-equipped Caterpillar D9G. 



85 



time -weigh ted average noise level as 
approximately 90 dBA. This dozer, there- 
fore, could be operated for a full 8-h 
shift. 



Subsequent inspection visits indicated 
that the reduced noise levels could be 
maintained with relatively minor mainte- 
nance of the elastomeric seals. 



TABLE 5. - Summary of noise control treatments involved 
on dozer with cab (high idle, doors closed) 







Sound level. 


Noise reduction 


No. 


Treatment 


dBA 


from baseline, 
dBA 


1 


None (baseline) 


100 





2 


Absorption under FOPS 


98 


2 


3 


Absorption and cab wall seals.. 


97.5 


2.5 


4 


Treatment 3, plus floormats and 










95.5 


4.5 


5 


Treatment 4, plus seat seals, 
hydraulic tank cover seals. 








and blade control seal 


93.5 


6.5 


6 


Treatment 5, plus dashboard 








treatment 


89 


11 




FIGURE 2. - Noise-controlled cab-equipped Caterpillar D9G. 



86 



SUMMARY 



1. The Bureau has demonstrated feasi- 
ble retrofit noise control technology 
for bulldozers commonly used in surface 
mining. 

2. The noise control treatments can be 
copied or adapted for their specific 
conditions by any surface mine in the 
country, using commercially available 
materials. 

3. The noise control technology was 
extended to rubber-tired front-end load- 
ers. The Bureau sponsored a research 
project that demonstrated the new 
application. 

4. The results of the bulldozer noise 
control project have been disseminated to 



the mining industry through a series of 
technology transfer workshops that were 
presented throughout the country. De- 
tailed instructions, in terms of illus- 
trated technical manuals and shop-quality 
drawings , are available in limited quan- 
tities from the Bureau. Single copies of 
the bulldozer noise control manual or the 
front-end loader noise control manual can 
be requested, in writing, from the Bureau 
of Mines, Pittsburgh Research Center, 
P.O. Box 18070, Pittsburgh, PA 15236. 
Each manual contains detailed instruc- 
tions on fabrication and installation of 
the noise control treatments. The manu- 
als also contain useful information on 
current Federal noise regulations , noise 
measurement techniques and instrumenta- 
tion, and materials suppliers. 



87 



IMPROVED HAUL ROAD BERM DESIGN 
By Gregory G. Miller, ^ Gary L. Stecklein,^ and John J. Labra^ 

INTRODUCTION 



Parts 55 and 77 of the Code of Federal 
Regulations, Title 30 — Mineral Resources, 
require that "berms or guards be provided 
on the outer bank of elevated roadways" 
at metal and nonmetal open pit mines and 
at surface coal mines to prevent haulage 
vehicles from running off the haul road. 
The proper design and construction of 
haul road berms are not known, other than 
the current rule-of-thumb recommendation 
that berms be built as high as the axle 
height of the largest haulage truck using 
the haul road. However, interviews with 
mine personnel indicate that berms built 
to this height are ineffective in stop- 
ping runaway vehicles. 

A wide variety of restraint systems 
are available. These systems are edge- 
of-road berms, guardrails, boulders. 



concrete barriers, median berms, and es- 
cape lanes. Mine operators overwhelming- 
ly prefer berms constructed of waste ma- 
terial because they feel that they are 
the least costly system since the waste 
material has to be transported along the 
haul road anyway. While the cost of the 
berm material may be negligible, addi- 
tional costs are incurred owing to con- 
struction time and additional road width 
necessary to carry the berm. 

To determine the proper design of safe 
haul road restraint systems, research was 
conducted by Southwest Research Insti- 
tute** for the Bureau of Mines on design 
requirements for edge-of-road berms , 
guardrails, boulders, concrete barriers, 
median berms, and escape lanes. 



LOCATION OF RESTRAINT SYSTEMS 



Restraint systems such as berms should 
be used on all elevated roadways to pre- 
vent vehicles from going over the road 
edge embankment. The design requirements 
are dependent on the maximum possible 
runaway vehicle approach conditions. It 
is obvious that certain locations along 



the roadway such as downgrades and sharp 
turns must have restraint systems, but 
since mechanical failure, adverse weath- 
er, or human error can cause accidents, 
flat elevated roadways also must have 
them. 



METHODS OF VEHICLE-BARRIER INTERACTION ANALYSIS 



To determine the effectiveness of vari- 
ous restraint systems, the following ap- 
proach was used: 

1. Geometric-scale model simulations. 

2. Full-scale field tests. 

^Mechanical engineer, Spokane Research 
Center, Bureau of Mines, Spokane, WA. 

^Mechanical engineer. Southwest Re- 
search Institute, San Antonio, TX. 

^Computer analyst. Southwest Research 
Institute, San Antonio, TX. 



3. Computer simulation. 

The runaway vehicle approach conditions 
of 30 mph and a 30° impact were consid- 
ered maximum. While the speeds of most 
runaway haulage vehicles are lower, a 
berm designed to withstand these impact 

'^Stecklein, G. L. , and J. Labra. Haul- 
road Berm and Guardrail Design Study 
and Demonstration. Volume I (contract 
HO282028, Southwest Res. Inst.). BuMines 
OFR 188-82, 1981, 186 pp.; NTIS PB 83- 
137091. 



88 



conditions will perform satisfactor- 
ily for either a lesser speed or a 
shallower impact angle. Since a loaded 
vehicle would impose the more stringent 
strength requirements on the berm, only 
the responses of loaded vehicles were 
evaluated. 

GEOMETRIC-SCALE MODEL SIMULATIONS 

Scale models of haulage trucks , edge- 
of-road berms , median berms , and escape 
lanes were constructed to provide corre- 
lation between field tests and computer 
simulation. The 35-, 85-, and 170-ton 
haulage trucks were selected as being a 
representative cross section of the haul- 
age vehicle population. Using simili- 
tude, 1/20-scale model haulage trucks 
were constructed for each size truck. 
The primary parameters of interest were 
the mass moments of inertia about the 
roll, pitch, and yaw axes. These inertia 
values were not available from the truck 
manufacturers and therefore were deter- 
mined experimentally since they were 
essential for determining the proper dis- 
tribution of mass during model construc- 
tion. The model trucks were fabricated 
using these data and truck manufacturer 
data. 

For truck modeling purposes, small 
double-acting cylinders simulated the 
commonly used nitrogen-over-oil sus- 
pension. For practical purposes, rigid 
rather than pneumatic tires were used on 
the model. A locked steering system was 
used to represent vehicles without 
steering-turn self -correction. No at- 
tempt was made to model body strength. 
Ground clearances and general configura- 
tion of the haulage truck were modeled. 
Vehicle weight distribution, sprung and 
unsprung masses, and suspension charac- 
teristics were scaled from values ob- 
tained from various manufacturers. 

Berm composition is different at every 
mine. To simulate the spectrum of possi- 
ble berm compositions, scaled unconsoli- 
dated and rigid berms were investigated. 



The unconsolidated berm was represented 
by a loose deposit of soil uniformly dis- 
tributed to a specific height. Compacted 
clay material was used to represent a 
rigid berm. Model tests were also run at 
intermediate berm strengths. 

FULL-SCALE FIELD TESTS 

Field tests of haul road berms were con- 
ducted using a 35-ton haul truck. The 
relative ability of this material to re- 
strain a 35-ton haul truck under varying 
approach conditions, berm heights, and 
compaction conditions was tested. Data 
collected included tire sinkage, wheel 
climb, and penetration along the direc- 
tion of travel (fig. 1). Economic con- 
straints of the field test program pro- 
hibited testing that would result in 
damage to the vehicle. As a result, 
small approach velocities were tested at 
various approach angles and then in- 
creased to the point where safety of the 
test was questionable. Results of the 
field test did not provide the informa- 
tion needed to predict the approach con- 
ditions at which rollover will occur. 
The field test information is, however, 
the basis for determining the correlation 
between the computer simulations and the 
scale model simulations. 

. COMPUTER SIMULATIONS 

Computer simulations of vehicles in- 
teracting with edge-of-road berms were 
performed using a highway-vehicle- 
object-simulation model (HV0SM).5 This 
program predicts the response of a 
vehicle and the forces generated during 
the vehicle's interaction with a rigid 
nondef lecting surface as a function 
of vehicle impact speed and approach 
angle. 

^Segal, D. J. Highway-Vehicle-Object- 
Simulation Model — 1976. Vol. 4, Engi- 
neering Manual — Validation. Calspan 
Corp. , Buffalo, NY, Report FHWA-RD-76- 
165, Feb. 1976, 460 pp. 



89 



EDGE-OF-ROAD BERMS 



An edge-of-road berm Is a mound of 
earth, usually constructed of mine waste, 
placed along the outer edge of an ele- 
vated roadway to prevent a runaway vehi- 
cle from leaving the roadway. Model 
tests, field tests, and computer analyses 
were used to determine how such berms 
should be constructed. 

Berms are currently constructed of a 
wide range of overburden material. A 
rear-dump truck backs perpendicular to 
the road edge and dumps successive mounds 
of spoil along the road edge. The over- 
burden material can consist of rock 12 to 
18 in. in size mixed with soil. There 
are no special soil grading (sizing) pro- 
cedures used to select berm material. 
The final shaping of the berm can be per- 
formed by a small front-end loader. If 
necessary, the bucket of the loader is 
used to tamp the berm material. Erosion 
of berms is a problem in areas with fre- 
quent or heavy rainfall. In these areas, 




Tire sinkage 




FIGURE 1. - Configuration of edge-of-road bar 



some berms are seeded to minimize erosion 
damage . 

All earthen berms deform during impact 
by a vehicle. Analyses show that failure 
occurs when the berm is too small or too 
weak. A large runaway haulage vehicle 
can easily plow through or over such a 
berm. There is the possibility of a 
slope failure of the road edge when a 
haulage truck penetrates too far into 
the berm. Therefore, to prevent a haul- 
age vehicle from coming too close to the 
road edge during collision with a berm, 
the berm is said to have failed when a 
vehicle's leading tire penetrates more 
than halfway through it . In this in- 
stance, the vehicle has "vaulted" the 
berm (fig. 1). 

To prevent the vehicle from vaulting 
the berm, berms must be constructed 
to a height-versus-strength relationship 
that will assure vehicle restraint by 
redirection, penetration, berm climb, or 
rollover. 

Redirection occurs when a vehicle in- 
teracts with a berm or barrier, usually 
at a shallow angle, and climbs it, only 
to slide down again to the roadway be- 
cause of insufficient frictional contact. 
Penetration occurs when a vehicle con- 
tacts a weak berm and is stopped by the 
soil resistance forces created by the 
vehicle tires and body plowing through 
the berm. Climb occurs when a berm has 
sufficient strength to allow a vehicle to 
ride up the berm. The change in the ele- 
vation during climbing will cause the 
vehicle to stop. 

Collision with a deformable berm is 
usually a combination of penetration and 
climb; as the leading vehicle tire pene- 
trates the berm, the tire sinks, increas- 
ing rolling resistance, while climbing 
the berm. To prevent a vehicle from 
leaving an elevated roadway, a properly 
designed berm must be constructed with 
its onboard face at an angle that will 
cause a vehicle to roll over onto the 
roadway if the vehicle exceeds the 



90 



designed stopping potential of the berm. 
Rolling over onto the roadway is deemed 
better than vaulting over an elevated 
roadway. 

A rigidly constructed berm represents 
an approximation of the minimum berm 
height required to restrain an errant 
haulage vehicle. Impacting a similar 
size berm constructed from a deformable 
material will result in a vehicle either 
penetrating the berm or vaulting over it. 
While the deformable material will offer 
increased rolling resistance, its reduced 
strength may allow a shear failure of the 
berm tip resulting from vehicle loading. 
Therefore, the smaller the berm size, the 
more rigid it must be. 

Curves were prepared for the 35-, 85-, 
and 170-ton haulage trucks from the scale 
model simulations , computer simulations , 
and full-scale field tests. A convenient 
way of presenting the predicted berm 
height is as a multiple of the axle 
height of the largest haulage vehicle 
using the roadway. When this ratio is 
plotted against the tire sinkage value 
that corresponds to berm strength, typi- 
cal curves represented in figure 2 re- 
sult. When the berm is weak, a large 
berm height is required to stop an errant 
vehicle through the mechanism of berm 
climb and berm penetration. At interme- 
diate berm strength, the kinetic energy 
of the vehicle is absorbed by berm climb, 
berm penetration, and, eventually, roll- 
over; but now a much smaller berm is re- 
quired. The smallest berm that can re- 
strain a runaway vehicle has its strength 
increased by compaction. The smallest 
berm is the most economical to build be- 
cause it does not require the excessive 
road width required by weak berms . An 
ideal high-strength berm has no tire 
sinkage, and the energy of the vehicle is 
absorbed by berm climb, as exhibited by 
redirection at shallow approach angles or 
by rollover onto the roadway at speeds in 
excess of berm stopping capability. 

Figure 2 shows that the smallest allow- 
able deformable berm for a 35-ton truck 
is one that is three times the axle 



height at a strength of 3 in of tire 
sinkage measured at axle height on the 
berm. For an 85-ton truck, a three- 
times-axle-height berm is required at a 
strength of 2.3 in of tire sinkage mea- 
sured at axle height on the berm. For a 
170-ton truck, a four-times -axle-height 
deformable berm is required at a strength 
of 2.3 in of tire sinkage measured at 
axle height on the berm. These figures 
are conservative by at least one axle 
height over rigid berm requirements. 

As a result of these simulations, berm 
height recommendations, for significantly 
compacted berms , can be categorized by 
the vehicle size. For vehicles whose 
load-carrying capacity is 85 tons or 
less , the compacted berm height recommen- 
dation is specified to be three times 
axle height; for haulage vehicles larger 
than 85 tons , the compacted berm height 
recommendation is four times the axle 
height. 

Berms can be constructed and compacted 
in layers to meet these recommendations. 
The face of the berm should then be cut 
at a steep angle (40°) to minimize the 





II II 1 


^ 




KE - *" 


KE —rollover, 


KE — redirecti 


on. 




berm 


berm climb, 


rollover. 






climb, 


penetration 


berm climb 






penetration 








II 










il 


KEY 








Maximum approacli conditions 








30 mph, 30° 






l\ 


Berm slope. 40° 






w 








-^A 


tire width-18 in. 







axle heigt)t-30 in 


_ 




r^^ 


85-ton haulage vehicle. 






tire width-24 in. 




8 


~\ '"^V 


axle height-50 in 


~ 




\ V\ 17 0-ton haulage vetiicle 




6 


- \ "N\^ tire widtti-36 in, 


_ 




:^ 


^^^^ ^^'"^ height-57 in 


- 


4 


__J^^~--^^^___^-— ■ 


2 







II II 1 


L,^ 



20 10 5 4 3 2 

BERM STRENGTH AS DETERMINED 
BY TIRE SINKAGE, In 

FIGURE 2. - Berm size requirement as a func- 
tion of berm strength for 35-, 85-, and 170- 
ton haulage vehicles. (KE kinetic energy) 



91 



ramp effect of the berm. This could be a 
problem when berms contain a considerable 
amount of rock and very little soil. In 
such cases using material with a specific 
grade (size) mix may be necessary. 



This may be accomplished by maintaining a 
full load in the vehicle during the tire 
sinkage tests and by removing the surface 
layer of the berm, which may cause erro- 
neous strength values. 



QUALIFYING A BERM 

Tire sinkage values obtained during 
the field tests were found to be repre- 
sentative of the berm strength and can 
be used for quantifying the berm size 
recommendations. The tire sinkage val- 
ues are, however, somewhat subject to 
the surface condition of the berm. 
Therefore, care must be taken to assure 
that the surface effects are negligible. 



A field technique for qualifying a berm 
for its capability in restraining a haul- 
age vehicle is to drive a fully loaded 
vehicle forward up a berm at a 45° angle 
to a height equal to the axle height of 
the vehicle and then record the tire 
sinkage value (fig. 3). The value may 
then be checked against the size-strength 
curves of figure 2 to see if the berm is 
acceptable. 



GUARDRAILS 



Generally, berms constructed from 
available mine waste material will be 
less expensive than a guardrail installa- 
tion. However, there are cases where a 
guardrail may be needed. For example, 
placing a guardrail along a haulage road 
that is too narrow to construct an ade- 
quate sized berm on may be less costly 
than widening the road. 

The Barrier VII computer program^ was 
used to evaluate various guardrail 



configurations. This program predicts 
the response characteristics of the vehi- 
cle, the deformation of the restraining 
structure, and the damage generated by 
the impact of the haulage vehicle. The 
result of a properly designed guardrail 
is the redirection of the errant vehicle. 

^Powell, C. H. Barrier VII: A Comput- 
er Program for Evaluation of Automobile 
Barrier Systems. Univ. CA, Berkeley, CA, 
Report UC SESM 70-17, Aug. 1970, 210 pp. 




Tire sinkage 



height -■ 



Axle 

FIGURE 3. - Berm qualification test at a 45° vehicle approach angle. 



92 



Guardrails varying from a triple tubu- 
lar beam to a simple I-beam or wooden 
post design were analyzed for effec- 
tive restraint of haulage vehicles. 
The choice of a particular guardrail 
design depends on the vehicle's size, 
velocity, and angle of approach. In- 
stallation costs of guardrail limit 
their application to situations where 
there may not be enough room for berm 
construction, or where the installa- 
tion may be considered permanent, 
such that higher initial cost can be 



justified on the basis of 
nance costs. 



lower mainte- 



A guardrail system was considered safe 
if its maximum rail deflection did not 
exceed half the width of the vehicle 
track (axle). For systems with shallow 
embedded posts, the barrier damage was 
more extensive than for those with ex- 
treme post depth. Table 1 is a summary 
of guardrail design concepts. Design 
specifications for table 1 are available 
from the work cited in footnote 4. 



BARRIERS 



A barrier is a berm with a near- 
vertical face constructed of material 
that is capable of absorbing the kinetic 
energy of a runaway vehicle by the 



displacement of the berm itself, and the 
reaction between the berm and the road 
surface. There are two major types of 
barriers: (1) A rigid barrier made of 



TABLE 1. - Summary of maximum approach conditions of rear-dump mine haulage 
trucks for guardrail design concepts 



Approach | CSl' I Conf iguration^ 


Approach | CSI^ I Conf iguration^ 


137,000-LB GROSS VEHICLE WEIGHT (GVW) , 


541,000-LB GVW, 170-TON CAPACITY 


35-TON CAPACITY 


10 mph at 7° 

20 mph at 13° 

30 mph at 16° 

30 mph at 29° 

35 mph at 35° 

35 mph at 46° 

35 mph at 58° 


100 
500 
1,000 
2,000 
3,000 
4,000 
5,000 


A 


10 mph at 14° 

20 mph at 28° 

30 mph at 36° 

35 mph at 62° 


100 

500 

1,000 

2,000 


A 

B, H 

C, I 
D 


B, H 

C, I 
D 

E, F 


323,800-LB GVW, 85-TON CAPACITY 


J, K 


10 mph at 8° 

20 mph at 17° 

30 mph at 21° 

35 mph at 33° 

35 mph at 47° 

35 mph at 65° 


100 
500 
1,000 
2,000 
3,000 
4,000 


A 

B, H 

C, I 
D 

E, F 
J, K 


J, K 



CSI = Collision severity index, an empirically derived relationship commonly used 
for guardrail evaluation. It provides a numerical comparison of the demands placed 
on a barrier system as a function of the vehicle's mass, mass moment of inertia, im- 
pact speed, and approach angle. 

^Configurations are defined as follows: 



Double 3-tube guardrail with 60-in-high 
wood posts — 



Single, wide, multiflange guardrail with 
60-in-high posts — 



A 72 in deep, 12 in wide. 

B 120 in deep, 12 in wide. 

C 144 in deep, 12 in wide, 

D 168 in deep, 14 in wide. 

E 120 in deep (with 10-ft by 28-in 

soil plate), 14 in wide. 
F 120 in deep (wide soil backup mass 

of 5 tons per foot), 14 in wide. 



H 72 in deep, 12 in wide. 
I 120 in deep, 12 in wide. 
J 168 in deep, 14 in wide. 

Single, wide, multiflange guardrail with 
60-in-high concrete posts — 

K 120 in deep, 20 in wide. 



93 



concrete and earth, and (2) an encased 
barrier such as barrels , membranes , or 
shotcrete-encased earth. The design ob- 
jective of barriers is to eliminate the 
possibility of a vehicle vaulting the 
berm, and to either redirect or arrest 
the motion of the vehicle. This is ac- 
complished by providing a near-vertical 
berm face, with the energy of the vehicle 
impact being dissipated by displacement 
of the berm and the berm reaction with 
the road surface. 

The advantages of the rigid-type bar- 
riers are (1) they can be designed to 
withstand severe impact without penetra- 
tion, (2) they can be designed to cause 
negligible vehicle damage for impacts of 
low severity, and (3) they can be reused 
at other locations. The disadvantages 
are (1) that rigid barriers are relative- 
ly unyielding and tend to aggravate the 
deceleration environment of the vehicle 
occupant and (2) their material and in- 
stallation cost is higher than that of 
conventional berms . 



The advantages of the encased barriers 
are (1) reduced material cost compared 
to rigid barriers and (2) the yield- 
ing action of the encased berm will 
provide a less severe deceleration en- 
vironment for the vehicle occupant. 
The disadvantages are (1) corrosion of 
the metallic elements resulting in main- 
tenance problems and need for peri- 
odic inspection, if plastic barrels are 
not used, (2) labor requirements to con- 
struct the system, and (3) the encased 
barrier system would not be salvable 
for reuse. 

Computer analysis shows that barriers 
can provide effective vehicle restraint 
for the range of approach conditions and 
vehicle sizes studied during this proj- 
ect. Barriers should be used only in 
areas where maintenance of the restraint 
system will cause a great economic bur- 
den, such as heavily traveled, permanent 
haul roads . 



BOULDERS 



Large rocks (18 to 24 in) and large 
boulders (3 to 4 ft in diameter) are used 
as edge-of-road berms in quarries and are 
placed 4 to 8 ft from the edge of the 
road. A minesite visited had two inci- 
dents of vehicles being restrained by a 
boulder-type berm. In both cases , the 
vehicle was unloaded and appeared to have 
been stopped by high-centering on a boul- 
der. Boulders would be used more often 
in eastern coal mines, but they are nor- 
mally used as the rock core in the valley 
fill for improved drainage. 

The ability of a berm constructed from 
a continuous line of large boulders to 
restrain or redirect a runaway vehicle 
was evaluated. Typically, and also for- 
tunately, a vehicle impacting a row of 
boulders or a berm constructed from sev- 
eral large boulders is not stopped in- 
stantaneously. The vehicle's kinetic, 
rotational, and potential energy is dis- 
sipated in the work generated as the 
boulders slide along the road surface. 
The primary area of concern is the 



distance associated with stopping various 
size vehicles by using typical-size boul- 
ders. It was assumed that boulders are 
not capable of developing a force suffi- 
cient to redirect a vehicle. Analysis 
shows that if boulders are sized to stop 
a vehicle in a short distance, they will 
probably cause considerable damage. If 
they are sized to reduce the deceleration 
forces, the distance that they must be 
placed from the edge of the road must 
increase. For example, if an empty 85- 
ton vehicle impacted a boulder berm at 20 
mph and 20° , it would push the impacted 
boulders 80 ft along the impact angle. 
This distance would necessitate position- 
ing the boulders about 25 ft from the 
edge of the road. 

Therefore, boulders are not considered 
to be a very effective means of providing 
vehicle restraint, the main reason being 
the damage that may be incurred by the 
vehicle. A viable alternative to the 
independent use of boulders is the burial 
of the boulders in an earthen berm. In 



94 



this way, the boulders act to make the 
berm more rigid while eliminating the 
required boulder push distance. The 



severity of impact is also significantly 
reduced. 



MEDIAN BERMS 



Median berms are unconsolidated mate- 
rial placed in the center of a haul road 
and are constructed in a manner that 
allows a runaway vehicle to straddle 
them, shearing off the portion of the 
berm above the vehicle's undercarriage, 
and eventually allowing the vehicle to 
come to a rest. The force required to 
shear the berm is dependent upon soil 
properties. 

Median berms can be constructed narrow 
or wide. A wide berm allows the vehicle 
to straddle the berm, and its tires to 
roll on the lower berm material. In this 
way, increased rolling resistance of the 
soft berm material allows the vehicle to 
stop quicker. However, model tests have 
shown that straddling a wide berm can re- 
sult in a vehicle overturning. 



Additional tests were conducted employ- 
ing a narrow berm that allowed the vehi- 
cle's rear track (axle) to completely 
straddle the berm. This requires some 
compaction of the berm to retain its de- 
sired height. The narrow berm stopped 
the vehicle in a shorter distance, par- 
ticularly at higher impact speeds (fig. 
4). The increased shear area and, to a 
lesser extent, the shear strength of the 
compacted material were responsible for 
the reduction in travel. Turning and 
misalignment of the vehicle were mini- 
mized by the restraining action of the 
narrow berm. 

Based on the results of these model 
tests, a narrow compacted median berm is 
recommended because of the decreased po- 
tential for rolling the vehicle over. 



40 


1 1 1 


1 1 J^ J' 


^ 


30 


- 


x^^!^i^^^ 


- 


20 


/^^ 


^^^^^^^ KEY 

-""^ 85-ton vehicle 
-8-pct grade 


- 




.^^y^^ A 


Compacted narrow berm- 1 20-pct load 






y^^^ V 


Compacted narrow berm- 0-pct load 




10 


y^^^ A 


Unconsolidated wide berm- 1 20-pct load 




yy^^ T 


Unconsolidated wide berm- 0-pct load 








Vehicle carrying load 






L a - ■ 


r\ 


^ \ 1 1 


Vehicle base carrying load 

1 1 1 1 





15 



30 45 60 75 90 

VEHICLE STOPPING DISTANCE, ft 



105 



120 



FIGURE 4. - Comparison of stopping distances on median berms for on 85-ton haulage vehicle on an 
-pet downgrade. 



95 



Entryways must be provided along the me- 
dian berm to allow the driver to align 
the vehicle with the berm. A road grader 



can shape the berm base to a width nar- 
rower than the vehicle's track. 



ESCAPE LANES 



The best alternative for effective 
vehicle restraint involves the use of es- 
cape lanes. They ideally perform their 
function without causing the vehicle to 
roll over. Model testing of an 85-ton 
vehicle was performed on an escape lane 
constructed of dry, fine-grained homogen- 
eous sand and a lane constructed of com- 
pacted fire clay. The arrangement of the 
model test consisted of (1) accelerating 
a scaled model vehicle down a curved ramp 
to obtain various entry velocities, 
(2) allowing the moving model to enter 
the escape lane test bed, and (3) measur- 
ing its stopping distance at the various 
entry velocities and escape lane slopes. 
Figure 5 shows a comparison of these 
tests on a sand test bed with theoretical 
analyses. Some escape lane recommenda- 
tions developed are — 



1. Entry to the lane 
by appropriate signs. 



should be marked 



Regardless of the material used, it must 
be free-draining so that freezing will be 
delayed during cold weather and it will 
not readily compact. It must also be a 
material that can be readily smoothed out 
after use and that can be maintained with 
a minimum of effort. 

7. The length of the escape lane 
should be based on the largest size vehi- 
cle traveling at a realistic maximum 
speed. The length of the lane will also 
be a function of the terrain; a lane lo- 
cated with a downslope would be longer 
than a lane located with an upgrade. 

8. A barrier constructed from sand, 
gravel, or any available overburden mate- 
rial should be positioned at the end of 
the escape lane to prevent a vehicle from 
traveling over an embankment, in the 
event the vehicle is not stopped in the 
escape lane area. 



2. Entry to the lane should be a 
smooth transition from the haulage road, 
thereby minimizing the steering require- 
ments of the operator. 

3. Width of the lane should be reason- 
ably greater than the width of the 
largest haulage vehicle. 

4. Depth of loose gravel or sand mate- 
rial should taper from a minimum at the 
entryway to two times the maximum ground 
clearance of any vehicle expected to uti- 
lize the escape lane. 

5. The depth of the arresting material 
should be graduated along the initial en- 
tryway of the ramp so that a vehicle will 
not be stopped too abruptly. 

6. Material used in the escape lane 
should be of an unconsolidating nature; 
pea gravel is the most common material 
used in public highway construction. 



9. The arrester bed material should 
also ensure that once a vehicle is 
stopped it will not roll back. Mainte- 
nance is necessary to keep the ramp in 
the proper condition. The ruts must be 
smoothed out and the surfacing material 
loosened frequently. As the material be- 
comes infiltrated with dirt and other 
fine materials, it must be removed and 
replaced with clean material. 

10. The optimum escape lane would con- 
sist of an uphill grade; however, in ac- 
tual practice, the required location may 
be along a downgrade having the necessary 
length for stopping the vehicle. 

11. Model tests showed that an escape 
lane with a median berm reduced the stop- 
ping distance approximately 50 pet for a 
fully loaded 85-ton vehicle traveling at 
40 mph. But since the median berm would 
be hard to maintain, it should be used 
where the escape lane length is limited. 



96 




10 20 3 40 50 60 70 80 90 100110120130 
VEHICLE STOPPING DISTANCE, ft 

FIGURE 5. - Stopping distances for an 85-ton haulage vehicle on an escape lane impacting at 
various velocities on a 20-pct positive grade. 

SUMMARY 



Edge-of-road berms , guardrails , boul- 
ders , concrete barriers, median berms, 
and escape lanes were evaluated for their 
ability to redirect, restrain, or roll 
over onto the roadway a runaway haulage 
vehicle. Geometric-scale model simula- 
tions, full-scale field tests, and com- 
puter simulations were used, where possi- 
ble, to evaluate each restraint system 
design at vehicle approach conditions of 



30 mph, 30° impact, and carrying a full 
payload. 

The results of this study indicate that 
the construction requirements of berms 
can be directly related to the size of 
the largest vehicle to be restrained, and 
the composition and state of compaction 
of the berm material. For significantly 
compacted berms , it is recommended that 



97 



berms be constructed to three times axle 
height for vehicles of 85 tons capacity 
or less; for vehicles larger than 85 
tons, the berms should be constructed to 
four times axle height. Berms must be 
constructed to slopes greater than 40°. 
When berms cannot be constructed to a 
significant state of compaction, as indi- 
cated by tire sinkage qualification 
tests, the size of the berm must be in- 
creased according to the included recom- 
mendations to properly restrain a runaway 
haulage vehicle. 

The choice of a particular guardrail 
design depends on the vehicle size, ve- 
locity, and angle of approach. Guardrail 
configurations were analyzed for their 
capability to redirect 35-, 85-, and 170- 
ton loaded haulage vehicles traveling up 
to 35 mph with a 60° approach angle. Al- 
though guardrails can redirect a large 
haulage vehicle, they are generally too 
expensive for normal haul road use and 
are restricted to permanent or narrow 
elevated roadways. 

Barriers eliminate the possibility of a 
vehicle vaulting a berm. The vehicle is 
either redirected or stopped by the bar- 
rier's near-vertical face. Rigid bar- 
riers are almost indestructible and can 
be reused, but because of their high ini- 
tial cost, their use is restricted to 
permanent or narrow elevated roadways, as 
in the case of guardrails. 



A berm constructed from a continuous 
line of large boulders was evaluated. A 
runaway vehicle is stopped by impacting 
and pushing the boulders along the 
road surface. Analysis shows that too 
large a boulder will cause excessive dam- 
age to the vehicle upon impact; however, 
a boulder of acceptable size requires a 
considerable push distance. Therefore, 
boulders are not considered to be an ef- 
fective restraint system unless they are 
buried in an earthen berm. 

Median berms are sometimes placed in 
the center of a haul road to act as an 
additional restraining system. Analysis 
shows that a narrow compacted median berm 
is recommended over a wide median berm 
because it provides a shorter stopping 
distance and a reduced rollover potential 
when straddled by the runaway haulage 
vehicle. 

Escape lanes are the best restraining 
system because they can stop a vehicle 
without rolling it over and without dam- 
aging it. The escape lane should be 25 
pet wider than the truck and be con- 
structed of loose draining gravel, with a 
depth that varies from a minimum at the 
entrance to twice the truck's ground 
clearance at the vehicle's estimated 
stopping distance to prevent abrupt stops 
and rollback. 



■Cr\J.S. GOVERNMENT PRINTING OFFICE: 1983-605-015/48 



JT.-BU.OF MINES, PGH., PA. 27 C 



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